Determining the amount of an analyte in plasma based on the measurement of the amount of the analyte in a whole blood sample

Abstract

Disclosed herein are embodiments of a method for calibrating a group of analyzer units, wherein each analyzer unit of the group of analyzer units is configured to determine the amount of an analyte in the plasma of a whole blood sample. The method includes providing a plurality of calibration whole blood samples, the plurality of calibration whole blood samples including calibration whole blood samples having respective hematocrit values; for each calibration whole blood sample of the plurality of calibration whole blood samples, measuring a hematocrit measurement value indicative of the hematocrit value of the calibration whole blood sample, measuring a whole blood measurement value indicative of the amount of the analyte in the calibration whole blood sample using at least one calibration analyzer unit of the group of analyzer units, measuring a plasma measurement value indicative of the amount of the analyte in the plasma of the calibration whole blood sample, and calculating a ratio between the whole blood measurement value and the plasma measurement value; generating a non-linear functional relationship between the calculated ratio and the corresponding hematocrit measurement value by curve fitting of a non-linear function parameterized by one or more calibration parameters, the curve fitting resulting in respective parameter values for each of the one or more calibration parameters; and storing an expression of the fitted non-linear function in each analyzer unit of the group of analyzer units to enable each analyzer unit of the group of analyzer units to calculate a hematocrit correction factor.

Description

Technical Field

[0001] The present invention relates to various aspects of determining the amount of an analyte in plasma based on the measurement of the amount of the analyte in a whole blood sample.

Background Art

[0002] Analytical device units for measuring the amount of an analyte in a blood sample using respective detectors or sensors are widely used in the medical and clinical fields. Such analytical device units are often simply referred to as analytical devices.

[0003] In addition to the general requirements in terms of accuracy, precision, and reliability, analytical device units for clinical applications are often subject to additional significant constraints. Such constraints include low operating costs, low downtime, ease of use, the need for high utilization efficiency, and in particular, the reduction of the need for sample preparation.

[0004] Many analytical device units perform measurements on biological samples containing blood with all components, particularly plasma and red blood cells. This has the advantage that the need for preprocessing the blood sample before performing the desired measurement is minimized, even if not completely eliminated. Generally, a blood sample containing both plasma and red blood cells is referred to as a "whole blood" sample.

[0005] Normally, the concentration of at least some analytes is defined as the concentration of the analyte in plasma. Therefore, the direct measurement of the concentration of an analyte in plasma based on a whole blood sample first requires separating the whole blood sample into plasma and other blood components, particularly red blood cells. However, this is a time-consuming process.

[0006] Therefore, it is desirable to directly determine the amount of an analyte in plasma from the measurement of the amount of the analyte in a whole blood sample. For this purpose, U.S. Patent No. 10,132,800 proposes a method for measuring the amount of an analyte in a whole blood sample, the method comprising the steps of measuring the hematocrit value of the whole blood sample, directly measuring the amount of analyte in the whole blood sample, and according to the relationship: D p =P a (D ST ,D H ) calculating a corrected amount of analyte, where in the formula, D p is the corrected amount of analyte, D ST is the measured amount of analyte, D H is the measured hematocrit value, P a is, as an indeterminate value, the measured amount of analyte D ST and the measured hematocrit value D H and is a polynomial of degree one or higher with indeterminate coefficients having polynomial coefficients depending on the analyte, the step comprising.

[0007] However, a multivariate polynomial having two independent variables requires a relatively large number of polynomial coefficients to be determined in the calibration process, thus complicating the process and being prone to overfitting. For example, even the lowest-order multivariate polynomial containing only a single cross-term contains four polynomial coefficients that need to be determined by calibration. SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] Therefore, it is still desirable to provide a method for measuring the amount of an analyte in a whole blood sample that is accurate and robust and requires little calibration effort or at least provides an alternative to known methods.

[0009] It is further desirable to provide a method for correcting the deviation of measurements on whole blood samples from corresponding measurements on plasma samples without the need for repeated calibration of individual analyzer units by the operator of the analyzer unit. Instead, it is desirable that applicable corrections can be determined during the design or manufacture of the device and / or associated assay, and that it can be transmitted to each analyzer unit.

Means for Solving the Problems

[0010] In such a background, according to a first aspect, disclosed herein is an embodiment of a method for calibrating a group of analyzer units, wherein each analyzer unit of the group of analyzer units is configured to determine the amount of an analyte in the plasma of a whole blood sample. Embodiments of the method are a) providing a plurality of calibration whole blood samples, the plurality of calibration whole blood samples including calibration whole blood samples each having a respective hematocrit value; b) for each calibration whole blood sample of the plurality of calibration whole blood samples, i) measuring a hematocrit measurement value indicating the hematocrit value of the calibration whole blood sample; ii) using at least one calibration analyzer unit of the group of analyzer units to measure a whole blood measurement value indicating the amount of analyte in the calibration whole blood sample; iii) measuring a plasma measurement value indicating the amount of analyte in the plasma of the calibration whole blood sample; iv) calculating a ratio of the whole blood measurement value to the plasma measurement value; c) generating a non-linear functional relationship between the calculated ratios and the corresponding hematocrit measurement values by curve fitting of a non-linear function parameterized by one or more calibration parameters, the curve fitting resulting in a respective parameter value for each of the one or more calibration parameters; d) A step of storing, in each analyzer unit of the group of analyzer units, an expression of a fitted non - linear function to enable each analyzer unit of the group of analyzer units to calculate a hematocrit correction factor including.

[0011] The expression of the fitted non - linear function is an expression of a parameterized non - linear function, and one or more calibration parameters have parameter values resulting from curve fitting. Once calibrated, each of the analyzer units of the group of analyzer units measures a whole - blood measurement value indicating the amount of analyte in a whole - blood sample and a hematocrit measurement value indicating the hematocrit value of the whole - blood sample. Then, from the hematocrit measurement value, and by determining a hematocrit correction factor from the stored expression of the fitted non - linear function including the fitted parameter values, and by applying the hematocrit correction factor to the whole - blood measurement value, the amount of analyte in the plasma of the whole - blood sample can be determined.

[0012] In particular, according to one aspect, what is disclosed herein is an embodiment of a method for measuring the amount of analyte in the plasma of a whole - blood sample. The method includes - a step of measuring a whole - blood measurement value indicating the measured amount of analyte in a whole - blood sample, - a step of measuring a hematocrit measurement value indicating the measured hematocrit value of the whole - blood sample, - a step of calculating a hematocrit correction factor from a stored expression of a fitted non - linear function of the measured hematocrit value, in particular, a fitted non - linear function parameterized by one or more calibration parameters having parameter values previously determined by performing the steps of the method for calibrating the group of analyzer units disclosed above and below, - a step of calculating the amount of analyte in the plasma by applying the calculated hematocrit correction factor to the whole - blood measurement value including.

[0013] Thus, the amount of analyte is calculated as a simple product or ratio of a measurement value indicating the measured amount of analyte in the whole blood sample and a hematocrit correction factor that depends on the measured hematocrit value. In particular, the hematocrit correction factor is derived from a fitted non-linear function of an indeterminate variable representing the hematocrit value, and the fitted non-linear function is parameterized by one or more calibration parameters. The parameter values of the one or more calibration parameters in the fitted non-linear function depend at least on the type of analyte and / or the type of assay used to measure the analyte.

[0014] In some embodiments, the non-linear function has only a single indeterminate variable, in particular, only the hematocrit value as the sole indeterminate variable, and thus, uses only a few calibration parameters to facilitate an accurate and robust calibration fit. In some embodiments, the non-linear function further depends on the measured amount of analyte, but preferably involves no more than three calibration parameters. Preferably, the calibration function is a non-polynomial function, such as including an exponential function.

[0015] In some embodiments, the non-linear function is parameterized by fewer than four calibration parameters, such as three or two calibration parameters or a single calibration parameter.

[0016] The inventors have noticed that this process provides an accurate determination of the amount of analyte in plasma for a wide range of analyte amounts and hematocrit values while reducing the risk of undesirable overfitting.

[0017] The step of calculating the hematocrit correction factor from the stored representation of the fitted non-linear function may include evaluating the fitted non-linear function at the measured hematocrit value, either by explicit calculation of the function value, or by look-up and optional interpolation in a look-up table, or in another suitable manner to obtain the function value of the fitted non-linear function at the measured hematocrit value. In particular, in some embodiments, the non-linear function is represented by a look-up table having hematocrit values as keys, optionally including interpolation. Applying the calculated hematocrit value to the whole blood measurement value may include multiplying the whole blood measurement value by the calculated hematocrit correction factor, or dividing the whole blood measurement value by the calculated hematocrit correction factor. This may depend on whether the ratio of whole blood and plasma measurements during calibration was calculated by dividing the whole blood measurement value by the corresponding plasma measurement value, or by dividing the plasma measurement value by the corresponding whole blood measurement value.

[0018] Preferably, the calibration process is performed using two or more calibration analyzer units to account for the expected differences between the analyzer units of the group of analyzer units. Thus, in some embodiments, step b) of the method for calibrating a group of analyzer units comprises, for each of the set of calibration analyzer units of the group of analyzer units, for each of the set of calibration whole blood samples of a plurality of whole blood samples, i) measuring a hematocrit measurement value indicating the hematocrit value of the calibration whole blood sample; ii) measuring, using the calibration analyzer unit, a whole blood measurement value indicating the amount of analyte in the calibration whole blood sample; iii) measuring a plasma measurement value indicating the amount of analyte in the plasma of the calibration whole blood sample; iv) calculating the ratio of the whole blood measurement value to the plasma measurement value and performing.

[0019] Preferably, the set of calibration analyzer units comprises two or more, for example more than 5, for example 3 to 20, for example 5 to 10, for example 6 to 10 calibration analyzer units. The calibration analyzer units can be used to perform measurements on the same set of calibration whole blood samples, or on each set of calibration whole blood samples.

[0020] In some embodiments, during calibration, the hematocrit measurement and / or the plasma measurement are measured by the same calibration analyzer unit that is used to measure the corresponding whole blood measurement of the calibration whole blood sample. For this purpose, the calibration plasma sample can be prepared from each calibration whole blood sample in a known manner, for example by centrifugation. The prepared calibration plasma sample can then be presented to the calibration analyzer unit for measurement of the plasma measurement indicating the amount of analyte in the plasma sample obtained from the original whole blood sample.

[0021] Thus, in some embodiments, generating a non-linear functional relationship by curve fitting involves generating a plurality of data points, each data point representing a corresponding calculated ratio of the hematocrit measurement of a calibration whole blood sample and the whole blood measurement measured by one of the set of calibration analyzer units for the calibration whole blood sample, and the corresponding plasma measurement measured by the same one of the set of calibration analyzer units. The corresponding plasma measurement is preferably measured on the plasma sample obtained from the calibration whole blood sample. The hematocrit measurement of the calibration whole blood sample is preferably measured using the same one of the set of calibration analyzer units as the corresponding whole blood measurement belonging to the same data point. Preferably, the curve fitting is based on the data points obtained using each of the set of calibration analyzer units and the data points obtained using each of the plurality of calibration whole blood samples.

[0022] In various embodiments, calibration parameters associated with a particular analyte are determined by curve fitting a parameterized non - linear function to a generated calibration data set. The calibration data set is derived from the measured analyte amounts of the particular analyte in a calibration whole - blood sample and in a corresponding plasma sample. The measured analyte amount of the particular analyte in the calibration whole - blood sample is obtained by one or more calibration analyzer units of the same group as the measurement analyzer unit used for subsequent measurements.

[0023] In some embodiments, the parameterized non - linear function is a non - linear non - polynomial function of the hematocrit value. In particular, in some embodiments, the non - linear non - polynomial function is an exponential function of the hematocrit value. The inventors have noticed that non - polynomial functions, particularly exponential functions, provide specific accurate correction factors with low - risk overfitting for at least some types of analytes. In some embodiments, the non - polynomial function is a function that is very different from a part of two polynomials.

[0024] In some embodiments, the hematocrit correction factor HCF(Hct) is HCF(Hct)=exp(f(Hct)) calculated from the measured hematocrit value Hct, where f(Hct) is a function of at least the measured hematocrit value Hct. In some embodiments, the function f is a parameterized function parameterized by one or more parameters. In some embodiments, the function f has Hct as its only indeterminate, but in other embodiments, the function f depends on one or more additional quantities to be determined, such as the temperature and / or concentration of the analyte.

[0025] In some embodiments, the hematocrit correction factor HCF(Hct) is with calibration parameters a and b HCF(Hct)=exp(a·Hct b ) It is calculated from the measured hematocrit value Hct. In some embodiments, the calibration parameter a has a parameter value of 2.0 to 2.4, such as 2.20 to 2.21, such as a = 2.204, and the calibration parameter b has a parameter value of 2.2 to 2.7, such as 2.4 to 2.5, such as 2.45 to 2.47, such as b = 2.468. In another embodiment, the calibration parameter a has a parameter value of 1.9 to 2.0, such as 1.96 to 1.97, and the calibration parameter b has a parameter value of 1.5 to 1.6, such as 1.53 to 1.54.

[0026] In some embodiments, the hematocrit correction factor HCF(Hct) involves calibration parameters a, b, and c, HCF(Hct)=exp(a·Hct b ·conc c ) is calculated from the measured hematocrit value Hct, where conc represents the measured amount of the analyte in the whole blood sample or an approximation thereof. In some embodiments, the calibration parameter a has a parameter value of 0.8 to 3.0, such as 1.5 to 2.0, such as 1.7 to 1.9. In some embodiments, the calibration parameter b has a parameter value of 1.5 to 2.0, such as 1.7 to 1.9. The parameter c can be selected from -0.01 to 1.5, such as -0.01 to 0.2, or 0.05 to 1.5. In some embodiments, the parameter c can be selected depending on the concentration conc. For example, the parameter c can be determined from a lookup table indexed for each concentration conc. In particular, each value of c can be associated with a different concentration range, or the parameter c can be determined by interpolation between parameter values obtained from a lookup table or by other methods. Thus, accurate calibration can be achieved using relatively few calibration parameters.

[0027] In some embodiments, measuring the whole blood measurement value and / or measuring the plasma measurement value includes using an immunoassay. The fitted non-linear function, and thus the hematocrit correction factor, may be specific to the type of immunoassay. The immunoassay may be provided in the form of a replaceable cartridge that can be inserted into the analyzer unit. The fitted non-linear function, and thus the hematocrit correction factor, is thus specific to the type of immunoassay, but is not specific to a particular analyzer unit as long as the analyzer unit belongs to a group of analyzer units that apply the fitted non-linear function, for example, all analyzer units of a particular manufacturer and model.

[0028] In some embodiments, the analyte is an antigen. In some embodiments, the analyte is cardiac troponin I. Thus, in some embodiments, the whole blood measurement value is obtained using a troponin I assay, particularly a high-sensitivity troponin I assay (hsTnI). Various embodiments of the methods disclosed herein provide accurate measurement of the analyte, particularly hsTnI, even when the whole blood sample is diluted only slightly. Thus, high sensitivity can be obtained. The inventors have noticed that the hematocrit correction factor for hsTnI as well as other analytes, such as NT-proBNP and / or others, can be accurately determined based only on the hematocrit, independent of the analyte concentration, particularly based on a non-linear function of only the hematocrit value as an indeterminate variable. In the case of some analytes, for example, procalcitonin (PCT), a non-linear function may be used independent of the analyte concentration, but a non-polynomial non-linear function that also depends on the analyte concentration may be particularly suitable.

[0029] The present disclosure relates to different aspects, corresponding devices, systems, methods, and / or products including the methods described above and below, each of which provides one or more of the benefits and advantages described in relation to one or more of the other aspects, each of which corresponds to one or more embodiments described in relation to one or more of the other aspects and / or disclosed in the appended claims.

[0030] In particular, according to one aspect, disclosed herein are embodiments of measuring the amount of an analyte in the plasma of a whole blood sample using a measurement analyzer unit of a group of analyzer units, the method comprising - providing a plurality of calibration whole blood samples, the plurality of calibration whole blood samples including calibration whole blood samples having respective hematocrit values; - for each calibration whole blood sample of the plurality of calibration whole blood samples, measuring a hematocrit measurement value indicative of the hematocrit value of the calibration whole blood sample, measuring a calibration whole blood measurement value indicative of the amount of analyte in the calibration whole blood sample using at least one calibration analyzer unit of the group of analyzer units, measuring a calibration plasma measurement value indicative of the amount of analyte in the plasma of the calibration whole blood sample, and calculating a ratio of the calibration whole blood measurement value to the calibration plasma measurement value; - generating a non-linear functional relationship between the calculated ratio and the corresponding hematocrit measurement value by curve fitting a non-linear function parameterized by one or more calibration parameters, the curve fitting resulting in respective parameter values for the one or more calibration parameters; - storing an expression of the fitted non-linear function in at least the measurement analyzer unit; - measuring, by the measurement analyzer unit, a whole blood measurement value indicative of the measured amount of analyte in the whole blood sample; - measuring, by the measurement analyzer unit, a hematocrit measurement value indicative of the measured hematocrit value of the whole blood sample; - calculating a hematocrit correction factor from a stored representation of a fitted non-linear function; - calculating the amount of analyte in plasma by applying the calculated hematocrit correction factor to the measured whole blood measurement value and including.

[0031] According to another aspect, disclosed herein is an embodiment of a computer-implemented method for determining the amount of analyte in plasma based on the measurement of the amount of analyte in a whole blood sample, the method comprising: - receiving a whole blood measurement value obtained by a measurement analyzer unit, the whole blood measurement value indicating the measured amount of analyte in the whole blood sample; - receiving a hematocrit measurement value obtained by the measurement analyzer unit, the hematocrit measurement value indicating the measured hematocrit value of the whole blood sample; - calculating a hematocrit correction factor from a stored representation of a fitted non-linear function of the measured hematocrit value, the fitted non-linear function being parameterized by one or more calibration parameters having parameter values previously determined by performing steps of a method for calibrating a group of analyzer units described above and below; - calculating the amount of analyte in plasma by applying the calculated hematocrit correction factor to the whole blood measurement value, in particular by multiplying or dividing the whole blood measurement value by the calculated hematocrit correction factor and including.

[0032] Furthermore, according to yet another aspect, disclosed herein are embodiments of a data processing system configured to perform the steps of the computer-implemented methods described herein. In particular, the data processing system may have program code stored therein that, when executed by the data processing system, causes the data processing system to perform the steps of the computer-implemented methods described herein. The data processing system may be embodied as a single computer or other data processing unit or device, or as a distributed system including a plurality of computers and / or other data processing devices, such as, for example, a client-server system, a cloud-based system, etc. The data processing system may include a data storage device for storing computer programs and / or sensor data.

[0033] In some embodiments, the data processing system is integrated into the analyzer unit, for example, as a suitably programmed internal data processing unit of the analyzer unit. In other embodiments, the data processing system may be a remote data processing system physically separate from the analyzer unit. For this purpose, the remote data processing system may include a communication interface for receiving measurement values from the analyzer unit, for example, directly from the analyzer unit or indirectly via one or more intermediate nodes, via a suitable wired or wireless connection.

[0034] According to one aspect, disclosed herein are embodiments of an analyzer unit for determining the amount of an analyte in the plasma of a whole blood sample, the analyzer unit comprising - an analyte sensor for measuring a whole blood measurement value indicative of the amount of the analyte in the whole blood sample, - a hematocrit sensor for measuring a hematocrit measurement value indicative of the hematocrit value of the whole blood sample, and - a data processing system as described above and below and.

[0035] The analysis device unit may be an analysis device unit of a group of analysis device units that are all calibrated by the methods described herein. In particular, all analysis device units of the group of analysis device units may store therein the representation of the same fitted non-linear function.

[0036] The group of analysis device units may comprise, or may consist of, analysis device units of the same manufacturer and model, or alternatively, a selected class of analysis device units that apply the same measurement protocol for measuring the analyte amount and thus can apply the same calibration. Thus, calibration may be performed as part of the design of a particular analysis device unit model and / or during the design of a particular measurement immunoassay to be used by a particular analysis device unit model for measuring a particular type of analyte.

[0037] In this regard, it should be understood that the parameterized non-linear function may be analyte-specific and / or specific to a particular type of immunoassay. However, the parameterized non-linear function may be applicable for a plurality of analysis device units, in particular for a given group of analysis device units such as analysis device units of a particular manufacturer and model.

[0038] The amount of analyte determined by the various embodiments of the process disclosed herein may be an absolute or relative amount, in particular the analyte concentration. Yet another aspect disclosed herein relates to an embodiment of a computer program configured to cause a data processing system to perform the acts of the computer-implemented methods described above and below. The computer program may comprise program code means adapted, when the program code means are executed on a data processing system, to cause the data processing system to perform the acts of the computer-implemented methods disclosed above and below. The computer program may be stored on a computer-readable storage medium, in particular a non-transitory storage medium, or embodied as a data signal. The non-transitory storage medium may include any suitable circuitry or device for storing data, such as RAM, ROM, EPROM, EEPROM, flash memory, magnetic or optical storage devices, e.g., CD ROM, DVD, hard disk, and / or the like.

[0039] Preferred embodiments will be described in more detail in connection with the accompanying drawings.

Brief Description of the Drawings

[0040]

Figure 1

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DETAILED DESCRIPTION OF THE INVENTION

[0041] FIG. 1 schematically illustrates an example of an analyzer unit generally designated 100. The analyzer unit includes an analyte sensor 130, a hematocrit sensor 120, and a processing unit 110.

[0042] It should be understood that the analyzer unit, not explicitly shown in FIG. 1, may include one or more additional components that are conventionally known in the field of analyzer units. Examples of such additional components include a sample inlet for receiving a blood sample, a fluid handling system for presenting the received blood sample to the analyte sensor and the hematocrit sensor, and the like. The analyzer unit may further include a suitable user interface that enables a user to interact with the analyzer unit. For this purpose, the user interface may include a display for presenting measurement results.

[0043] The analyte sensor 130 may use a suitable measurement methodology for measuring the concentration of one or more analytes in a whole blood sample. In particular, the analyte sensor may be configured to measure the concentration of the analyte by using an immunoassay as known in the technical field to which the present invention pertains. For this purpose, the analyte sensor may be a cartridge-based immunoassay sensor, and the analyzer may be configured to receive an assay cartridge 140. The cartridge may include a plurality of reagent cups 141.

[0044] In some embodiments, the immunoassay is based on dry chemistry concepts and a detection method based on non-intensified time-resolved fluorescence (TRF) technology. In this regard, the term dry chemistry means that the assay-specific reagents required, for example, including tracer antibodies, capture antibodies, and stabilizing reagents, are dry-coated into one or more assay-specific reagent cups 141 of the assay cartridge 140.

[0045] In one embodiment, each reagent cup is coated with streptavidin. The biotinylated capture antibody can be immobilized on the cup surface through the binding of streptavidin and biotin. Streptavidin and biotin form a strong non-covalent biological interaction. An insulating layer containing carbohydrates and all the specific additives required for the assay prevents any contact between the capture antibody and the tracer antibody. A europium-labeled tracer antibody can be added on top of the insulating layer.

[0046] Generally, the cups 141 can be pre-filled into the sealed cartridge 140, and each cartridge contains a plurality of cups, for example, 16 cups or another suitable number of cups. The cartridge can further include a desiccant in the pouch to control humidity. Each cup can be individually sealed in a separate chamber to extend the shelf life.

[0047] In some embodiments, in addition to the sample itself, the only other reagent required to perform the analysis is a buffer, particularly a liquid buffer, which may be the same for all tests. For this purpose, the analyzer unit can include a built-in solution pack, which can be a closed system containing the buffer in a bag and also has a container for the collection of both waste cups and liquid waste. This means that the user does not need to directly contact the sample or any used reagents.

[0048] The analyte sensor is configured to analyze a blood sample. The blood sample can be either whole blood or plasma. However, during normal use of the analyzer unit, for example, during clinical use, it is often preferred to perform measurements directly on whole blood samples so as to reduce the time and effort required for sample preparation prior to measurement. The sample can be received by the analyzer unit in a sample tube, particularly a closed sample tube. The analyzer unit can automatically perform aspiration from the closed sample tube. The analyzer unit can acquire a small amount of the sample and add the acquired sample to a reagent cup. The sample is typically diluted by a buffer. When the sample (and possibly the buffer) is added, it dissolves the insulating layer of the cup. This can occur over a relatively short time period, such as less than 15 seconds.

[0049] The cup can be incubated at a suitable temperature, such as 37 °C. During this incubation, an antibody-antigen-antibody "sandwich" complex is formed, and this complex remains immobilized at the bottom of the reagent cup by the capture antibody. The cup is washed and dried to remove all unbound materials. After drying, the analyte sensor 130 exposes the cup to excitation light and measures the europium reaction to the excitation light. The reaction can be expressed in counts per second or in another suitable manner. The reaction is proportional to the emitted photons, which are directly proportional to the amount of antigen present. Thus, the measured reaction can function as a measurement value indicating the concentration of the analyte in the sample. In particular, when the sample is a whole blood sample, the measured reaction can function as a whole blood measurement value indicating the concentration of the analyte in the whole blood sample. Similarly, when the sample is a plasma sample, the measured reaction can function as a plasma measurement value indicating the concentration of the analyte in the plasma sample, for example, the plasma sample of a corresponding whole blood sample, i.e., the plasma sample obtained from the corresponding whole blood sample.

[0050] It should be understood that other embodiments of the analyzer unit can include different types of analyte sensors configured to perform the measurement of analyte concentration in a different manner. The hematocrit sensor 120 can use a suitable measurement methodology to determine the hematocrit value of the received whole blood sample. This can be carried out in parallel with the assay measurement. Generally, the hematocrit value can be determined based on the automatic measurement of the electrical conductivity of the whole blood sample. In one embodiment, the conductivity is measured at two frequencies. Based on the measured conductivity, the Hct is determined and, optionally, the salt concentration of the sample is corrected. It should be understood that other embodiments of the analyzer unit may include different types of hematocrit sensors or may be configured to perform the measurement of the hematocrit value in a different manner.

[0051] The analyte sensor 130 and the hematocrit sensor 120 are communicatively coupled to the processing unit 110 and transfer their respective measurement results to the processing unit 110 for further processing. It should be understood that the sensors can transfer to the processing unit 110 a raw measurement signal or a pre-processed measurement signal or data, such as an A / D converted signal, a filtered signal, an amplified signal, and / or a separately pre-processed signal or data.

[0052] The processing unit 110 may include a suitable programmed CPU 111 and a data storage device 112. The processing unit 110 is configured to execute program code 113 to control the operation of the analyzer unit. The data storage device 112 may be a hard drive, an EEPROM, a solid state drive, or another suitable data storage device. The program code 113 may be stored therein. The processing unit 110 can thus read the program code 113 from the data storage device 112 to the CPU 111 and the CPU 111 can execute the read program code.

[0053] In particular, the program code 113 is configured to cause the processing unit 110 to process the measurement values in response to the measurement values acquired from the analyte sensor and the hematocrit sensor, and to present the processed measurement results to the user, for example, via a suitable display or in another form, and / or to communicate the processed measurement results to a remote data processing system. In various embodiments of the analyzer unit, the processing of the measurement values includes the calculation of the analyte concentration in plasma based on measurements performed on a whole blood sample as described herein. For this purpose, the data storage device 112 may store, for example, a representation 114 of a fitted non-linear function for use by the analyzer unit to calculate a hematocrit correction factor, as described in more detail below. It should be understood that the representation of the fitted non-linear function may be stored as part of a computer program or separately therefrom, for example, as a configuration file or in another suitable manner. In some embodiments, the computer program and the representation of the non-linear function may be stored on different storage devices. The representation of the non-linear function may also be accessed by the analyzer unit from a remote data storage device.

[0054] Figure 2 schematically illustrates a process for calibrating a group of analyzer units, e.g., analyzer units of the same manufacturer and model. Calibration process 300 is performed on a set of calibrated analyzer units and results in an expression of a fitted non-linear function representing a hematocrit-dependent correction factor for use by each analyzer unit of the group of analyzer units when performing measurement process 200 on a whole blood sample whose measurement result is to represent the analyte concentration in plasma. Thus, the expression of the fitted non-linear function can be stored in each of the analyzer units of the group. This can be done during the manufacture of the analyzer units. Alternatively, for example, when a new type of immunoassay is designed for use by an analyzer unit, an assay-specific calibration process 300 can be performed using a set of calibrated analyzer units, and the resulting expression of the newly fitted non-linear function can then be communicated to the analyzer units of the group. The expression of the fitted non-linear function can be delivered, for example, on a suitable data carrier or downloaded to individual analyzer units via a suitable computer network. It should be understood that the expression of the non-linear function can be specific to a particular type of immunoassay or at least to a particular type of analyte to be measured. However, for a particular assay or analyte, the expression of the non-linear function obtained during calibration as described herein is independent of the analyzer, i.e., applicable to all analyzer units of a given group, e.g., all analyzer units of the same manufacturer and model. Preferably, the obtained non-linear function is independent of the analyte concentration. Preferably, for at least some types of analyte / assay, the obtained non-linear function depends only on the hematocrit value. For other types of analyte / assay, a non-polynomial non-linear function that depends on the analyte concentration can be used.

[0055] It should be understood that the representation of a non - linear function can be in several ways, for example, as an executable function call that implements a mathematical function, optionally including interpolation between tabular function values, as a look - up table, or in another suitable manner, to represent the non - linear function.

[0056] It should be further understood that the calibration analysis device units of a set of calibration analysis device units need not necessarily be a particular one of the group of analysis device units, since calibration can preferably be transmitted from any one of the group of analysis device units to another.

[0057] Figure 3 schematically illustrates an example of a calibration process 300 and a subsequent measurement process 200. In the calibration process 300, the ratio R of whole blood to plasma is determined experimentally by comparing analyzer measurements from plasma samples and whole blood samples with varying hematocrit values.

[0058] In particular, in one embodiment, in an initial step S201, a plurality of calibration whole blood (WB) samples are obtained such that the calibration whole blood samples have hematocrit values that cover a relevant range, for example, a range of 10 - 70% or even 0 - 70%.

[0059] In step S202, the hematocrit value (Hct), or at least a hematocrit measurement value indicating the hematocrit value, and the whole blood analyte amount, or a whole blood measurement value (AWB) indicating the whole blood analyte amount, are directly measured in each of the plurality of calibration whole blood samples. The measurement is carried out, in particular, by a set of analyzer units selected, for example randomly, from the group of analyzer units to be calibrated, using a suitable immunoassay for measuring the analyte in question. For the purposes of this description, the analyzer units used to carry out the calibration process are also referred to as calibration analyzer units.

[0060] In step S203, the amount of plasma analyte (APL) in the plasma sample from each of the plurality of calibrated whole blood samples, or at least the plasma measurement value indicating the amount of plasma analyte, is measured. These measurements are also preferably carried out using the same calibration analyzer unit as the corresponding measurements of the whole blood analyte amount, using the same type of immunoassay.

[0061] In step S204, the process calculates the ratio R(Hct)=AWB / APL for plasma and whole blood samples having equal analyte concentrations, where AWB and APL are obtained by the same calibration analyzer unit. Each ratio is calculated for the plasma and whole blood analyte amounts measured using the selected set of calibration analyzer units.

[0062] In step S205, the process generates a parameterized non-linear, preferably non-polynomial, functional relationship between the discovered R value and Hct by curve fitting. Curve fitting may use any suitable fitting process, for example, a least squares fitting process. For this purpose, the non-linear functional relationship is parameterized by one or more calibration parameters, and the parameter values of these calibration parameters are determined by the curve fitting process, for example, calibration parameter a 1 ,…a n , with n>0, as R(Hct)=R(Hct|a 1 ,…,a n ).

[0063] In one particular embodiment, the analyte to be measured is cardiac troponin I, and the assay used to measure the cardiac troponin I concentration in the sample is a high-sensitivity troponin I assay (hsTnI). In the case of hsTnI, the following non-linear relationship: R hsTnI (Hct)=exp(-a·Hct b ) has been found to be appropriate with calibration parameters a and b.

[0064] In one example, the curve fitting process results in parameter values for calibration parameter a in the range of 2.0 to 2.4, such as 2.20 to 2.21, such as a = 2.204, and for calibration parameter b in the range of 2.2 to 2.7, such as 2.4 to 2.5, such as 2.45 to 2.47, such as b = 2.468.

[0065] The measured data, and an exemplary calibration non-linear fit 401 using the hsTnI assay, are illustrated in FIG. 4A. The non-linear fit is based on data points obtained from respective calibration samples having different hematocrit values and different analyte concentrations. Further, the non-linear fit is based on data points obtained using a plurality of calibration analyzer units, eight calibration analyzer units in this particular example.

[0066] For other analytes, for example, in the case of NT-proBNP, the above functional form may similarly be appropriate. For example, in the case of NT-proBNP, the following non-linear relationship: R NT proBNP = exp(−a·Hct b ) has been found to be suitable, where the calibration parameter a has parameter values in the range of 1.9 to 2.0, such as 1.96 to 1.97, and the calibration parameter b has parameter values in the range of 1.5 to 1.6, such as 1.53 to 1.54.

[0067] The measured data, and an exemplary calibration non-linear fit 402 using the NT-proBNP assay, are illustrated in FIG. 4B. The non-linear fit is based on data points obtained from respective calibration samples having different hematocrit values and different analyte concentrations. Further, the non-linear fit is based on data points obtained using a plurality of calibration analyzer units.

[0068] The above functional form using appropriately selected calibration parameter values may also be appropriate for other analytes. Further, for other analytes, other non-linear functional relationships may also be appropriate. For some analytes, a functional relationship that further depends on the analyte concentration may be more preferred. For example, in the case of PCT, the following functional relationship: R PCT = exp(−a·Hct b *AWB c ) has been found to be particularly suitable for at least the generally encountered range of analyte concentrations, where AWB is the measured whole blood value, or an approximation thereof, for example, a non-temperature corrected approximation of the measured whole blood value, and involves calibration parameters a, b, and c. In some embodiments, calibration parameter a has parameter values of 0.8 to 3.0, such as 1.5 to 2.0, such as 1.7 to 1.9. In some embodiments, calibration parameter b has parameter values of 1.5 to 2.0, such as 1.7 to 1.9. Parameter c can be selected between -0.01 and 1.5, such as -0.01 and 0.2, or 0.05 and 1.5. In some embodiments, parameter c can be selected depending on the concentration AWB. For example, parameter c can be determined from a look-up table indexed for each concentration AWB. In particular, each value of c can be associated with different concentration ranges, or parameter c can be determined by interpolation between parameter values obtained from the look-up table, or by other means.

[0069] The measured data, and the corresponding non-linear fit 403 of an exemplary calibration using the PCT assay, are illustrated in FIG. 4C. The non-linear fit is based on data points obtained for a given concentration range from each calibration sample having different hematocrit values, as well as the corresponding selection of c. Further, the non-linear fit is based on data points obtained using multiple calibration analyzer units.

[0070] Referring again to FIG. 3, in step S205, a lookup table for looking up and optionally complementing the representation of a computer program, e.g., a suitable function, or function values of a non-linear function, is generated for distribution to other analyzer units of the group of analyzer units to be calibrated.

[0071] Each of the group of analyzer units can subsequently determine the amount of analyte in plasma based on measurements on a whole blood sample for analytes to which the determined non-linear relationship is applicable. For this purpose, the analyzer unit used for measurement, also referred to herein as the measurement analyzer unit, can perform the following measurement process 300.

[0072] In an initial step S301, the hematocrit value Hct and the analyte amount AWB are directly measured in the whole blood sample to be analyzed by the measurement analyzer unit. In step S302, a hematocrit correction factor HCF(Hct) corresponding to the measured hematocrit value Hct is determined from the stored representation of the non-linear relationship, e.g.,

[0073]

Number

[0074] as determined. In step S303, the determined hematocrit correction factor HCF(Hct) is applied to the measured analyte amount AWB, in particular,

[0075]

Number

[0076] in accordance with, to obtain the corresponding plasma analyte amount. For example, in the case of the above example of correction factor R hsTnI and parameter values a = 2.204 and b = 2.468, the applicable conversion is APL = HCF·AWB = AWB / R hsTnI = AWB·exp(2.204·Hct 2.468 ) is as follows.

[0077] In step S304, the process outputs, for example, displays, the calculated plasma value APL of the analyte amount. In the above, embodiments of a method for directly measuring an analyte concentration in a whole blood sample have been described. In various embodiments of the methods and apparatuses disclosed herein, the analyte concentration can be measured interchangeably for whole blood and plasma samples. All reported analyte concentrations represent the analyte concentration in the plasma phase of the sample.

[0078] Therefore, it is not necessary to separate red blood cells from plasma, measure against plasma, or manually determine Hct and manually correct the measured analyte concentration in the whole blood sample. The measurement is performed automatically, the measurement is corrected, and thus only the corrected result is reported to the user. Furthermore, the calibration and correction described have been found to be accurate and reliable and involve only a few calibration parameters that need to be determined by fitting experimental data.

[0079] FIG. 5 shows the correlation between the calculated amount of analyte in plasma based on the measurement of the amount of analyte in a whole blood sample and the corresponding reference analyte concentration in plasma over a certain concentration range. As can be seen from FIG. 5, the method described herein results in an accurate determination of the amount of analyte in plasma over a wide range of concentrations. In particular, for at least some analytes / assays, it has been found that the correction factor determined as a function of only the hematocrit value is accurate independently of the analyte concentration.

[0080] Embodiments of at least some of the steps of the methods described herein may be computer-implemented. In particular, embodiments of at least some of the steps of the method may be implemented using hardware comprising several distinct elements and / or at least in part using a suitably programmed microprocessor. In apparatus claims listing several means, some of these means may be embodied by one and the same element, component, or item of hardware. The mere fact that certain measures are recited in mutually different dependent claims, or described in different embodiments, does not indicate that a combination of these measures cannot be used to advantage.

[0081] The term "comprising," as used herein, is taken to specify the presence of the stated features, elements, steps, or components but does not preclude the presence or addition of one or more other features, elements, steps, components, or groups thereof.

Claims

1. A method for calibrating a group of analyzer units, each analyzer unit of the group of analyzer units being configured to determine the amount of an analyte in the plasma of a whole blood sample, the method comprising: providing a plurality of calibration whole blood samples, each of the plurality of calibration whole blood samples including a calibration whole blood sample having a respective hematocrit value; for each calibration whole blood sample of the plurality of calibration whole blood samples, measuring a hematocrit measurement value indicative of the hematocrit value of the calibration whole blood sample, using at least one calibration analyzer unit of the group of analyzer units to measure a whole blood measurement value indicative of the amount of the analyte in the calibration whole blood sample, measuring a plasma measurement value indicative of the amount of the analyte in the plasma of the calibration whole blood sample, and calculating a ratio of the whole blood measurement value to the plasma measurement value; generating a non-linear functional relationship between the calculated ratio and the corresponding hematocrit measurement value by curve fitting of a non-linear function parameterized by one or more calibration parameters, the curve fitting resulting in respective parameter values of the one or more calibration parameters; storing an expression of the fitted non-linear function in each analyzer unit of the group of analyzer units to enable each analyzer unit of the group of analyzer units to calculate a hematocrit correction factor A method comprising.

2. A method for measuring the amount of an analyte in the plasma of a whole blood sample, comprising: measuring a whole blood measurement value indicative of the measured amount of the analyte in the whole blood sample; measuring a hematocrit measurement value indicative of the measured hematocrit value of the whole blood sample; calculating a hematocrit correction factor from a stored expression of a fitted non-linear function of the measured hematocrit value; calculating the amount of the analyte in the plasma by applying the calculated hematocrit correction factor to the whole blood measurement value A method comprising.

3. The method according to claim 1 or 2, wherein the fitted non-linear function is parameterized by less than four calibration parameters, such as two calibration parameters or a single calibration parameter.

4. The method according to any one of claims 1 to 3, wherein the fitted non-linear function is a non-linear non-polynomial function of the hematocrit value.

5. The method according to any one of claims 1 to 4, wherein the non-linear non-polynomial function is an exponential function of the hematocrit value.

6. The method according to any one of claims 1 to 5, wherein the analyte is an antigen.

7. The method according to any one of claims 1 to 6, wherein the analyte is cardiac troponin I.

8. The method according to claim 7, wherein the whole blood measurement value is obtained using a troponin I assay, particularly a high-sensitivity troponin I assay.

9. The method according to any one of claims 1 to 8, wherein the analyte is procalcitonin or NT-proBNP.

10. The hematocrit correction factor HCF is accompanied by calibration parameters a and b, HCF = exp(a · Hct ｂ ) and is calculated from the measured hematocrit value Hct as, the method according to any one of claims 1 to 9.

11. The calibration parameter a has a parameter value of 2.0 to 2.4, such as 2.20 to 2.21, and the calibration parameter b has a parameter value of 2.2 to 2.7, such as 2.4 to 2.5, such as 2.45 to 2.47, the method according to claim 10.

12. The calibration parameter a has a parameter value of 1.9 to 2.0, such as 1.96 to 1.97, and the calibration parameter b has a parameter value of 1.5 to 1.6, such as 1.53 to 1.54, the method according to claim 10.

13. The hematocrit correction factor HCF is accompanied by calibration parameters a, b, and c, HCF(Hct) = exp(a·Hct ｂ ·conc ｃ ) and is calculated from the measured hematocrit value Hct as, wherein c optionally depends on the analyte concentration conc, the method according to any one of claims 1 to 12.

14. A computer-implemented method for determining the amount of an analyte in plasma based on the measurement of the amount of the analyte in a whole blood sample, comprising: receiving a whole blood measurement value obtained by a measurement analyzer unit, wherein the whole blood measurement value indicates the measured amount of the analyte in the whole blood sample; receiving a hematocrit measurement value obtained by the measurement analyzer unit, wherein the hematocrit measurement value indicates the measured hematocrit value of the whole blood sample; A step of calculating a hematocrit correction factor from a stored representation of a fitted non-linear function of the measured hematocrit value, wherein the fitted non-linear function is parameterized by one or more calibration parameters; A step of calculating the amount of the analyte in the plasma by applying the calculated hematocrit correction factor to the whole blood measurement value; A method comprising:

15. A computer program including program code configured to cause the data processing system to perform the steps of the method according to claim 14 when executed by the data processing system.

16. A data processing system configured to perform the steps of the method according to claim 14.

17. An analyzer unit for determining the amount of an analyte in the plasma of a whole blood sample, comprising: An analyte sensor for measuring a whole blood measurement value indicating the amount of the analyte in the whole blood sample; A hematocrit sensor for measuring a hematocrit measurement value indicating the hematocrit value of the whole blood sample; The data processing system according to claim 16; And an analyzer unit.

18. The analyzer unit according to claim 17, further comprising a memory storing the representation of the fitted non-linear function.

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