Haematocrit Detection via Complex Capacitance Extrapolation
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Solution Overview
Problem
Current methods for determining haematocrit in blood samples, such as the Maxwell-Fricke method, are prone to errors due to reliance on accurate plasma resistance measurements, which can vary with electrolyte content and concentration, making them unsuitable for point-of-care devices.
Innovation Solution
A method using complex capacitance measurements, where a plurality of complex capacitance values are calculated and extrapolated to determine haematocrit, independent of assumed plasma resistance, by fitting a circular arc to capacitance data and using a calibration curve to derive haematocrit values, reducing sensitivity to salt and donor variability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the Maxwell-Fricke method is used to measure haematocrit, then the measurement can be performed with simple conductivity measurement, but the measurement precision deteriorates due to reliance on assumed plasma resistance values that vary with electrolyte content and concentration
Solution Approach 1:
The patent changes the measurement parameter from conductivity (real impedance) to capacitance (imaginary impedance). By measuring capacitance instead of conductivity, the method eliminates dependence on plasma resistance assumptions while maintaining measurement simplicity. The capacitance measurement at high frequency directly reflects erythrocyte concentration without being influenced by electrolyte variations in plasma.
2Ease of operation
If point of care devices use internally stored average plasma resistance values, then the device operation is simplified, but the measurement precision deteriorates due to errors introduced when plasma resistance deviates from average values
Solution Approach 1:
The patent extracts the measurement from dependence on plasma resistance by using capacitance measurement instead. The capacitance method isolates the erythrocyte signal from plasma properties, removing the need to know or assume plasma resistance values. This eliminates the source of error while keeping the device operationally simple.
3Measurement precision
If capacitance measurements are performed at multiple frequencies, then the measurement precision improves through circular arc fitting, but the device complexity increases due to multiple measurements required
Solution Approach 1:
The patent uses periodic action by performing measurements at multiple discrete frequency points. These periodic measurements at different frequencies generate data points that, when fitted to a circular arc, provide accurate capacitance values. The multi-frequency approach is systematic and can be implemented efficiently in point-of-care devices.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves haematocrit detection performance by minimizing errors associated with varying salt concentrations and plasma resistance, providing more accurate haematocrit and haemoglobin concentration measurements.
Implementation Method 1
capacitance is charge stored at an interface due to an applied potential
Implementation Method 2
εr is the relative static permittivity (generally referred to as the dielectric constant) of the liquid
Implementation Method 3
Capacitance is based on the charging/discharging process that can be caused by rearrangement of ions or oscillation of dipoles
Implementation Method 4
Capacitance is based on the charging/discharging process that can be caused by rearrangement of ions or oscillation of dipoles
Implementation Method 5
the complex capacitance depends on the potential applied and the time of perturbation i.e. the frequency of the input signal in an electrochemical impedance spectroscopy (EIS) measurement
Data Source
AI summary
A method of determining haematocrit or haemoglobin concentration of a blood sample comprises calculating, based on a plurality of complex capacitance values of the blood sample, a complex capacitance at a predetermined imaginary component value, each of the plurality of complex capacitance values of the blood sample having a corresponding frequency; and determining the haematocrit or haemoglobin concentration based on the calculated complex capacitance or a real component of the calculated complex capacitance.