Method for determining glomerular filtration rate in 16-17-year-old adolescents with chronic kidney disease

Abstract

FIELD: medicine.SUBSTANCE: invention relates to medicine, namely to pediatrics, and can be used to determine the glomerular filtration rate (GFR) in 16-17-year-old adolescents with chronic kidney disease. Blood samples are collected. In a 16-17-year-old adolescent, serum creatinine is measured in micromoles per liter, height is measured in centimeters, body weight is measured in kilograms, body mass index (BMI) is calculated, and physical activity levels are determined. The calculated level of cystatin C (rCystatin C), mg / l, is determined using the claimed formula.EFFECT: method provides an opportunity to increase the accuracy of determining the GFR in adolescents, as well as to reduce the difference in GFR when switching from pediatric to therapeutic formulas, using the results of a publicly available laboratory test, by determining: blood creatinine, height, weight, body mass index, and the level of physical activity of the adolescent, and determining the GFR based on the calculated cystatin C.1 cl, 1 dwg, 19 tbl, 6 ex

Description

[0001] Field of invention. The invention relates to medicine, specifically pediatrics, and can be used by pediatricians and nephrologists at medical institutions to determine the glomerular filtration rate (GFR) in adolescents with chronic kidney disease (CKD) before transitioning to the adult healthcare system.

[0002] Background of the art. Determination of SCF is necessary for the diagnosis of CKD and dynamic monitoring of patients with this condition, prognostication of the course of CKD, including the likelihood of complications, determination of the need and timing of initiation of renal replacement therapy, assessment of the safety of diagnostic procedures with contrast enhancement, etc. In accordance with international recommendations, SCF monitoring should be performed in all patients with CKD from 1 time per year to 1 time in 3 months and more often depending on the severity of the disease [Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group.KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int. 2024;105(4S):S117-S314]. Therefore, to determine the SCF, a generally available method is needed that is technically simple, does not require high-tech resource support, does not require additional invasive procedures and has no complications [Clinical guidelines.Chronic kidney disease (CKD). Approval date: 2024 [https: / / cr.minzdrav.gov.ru / preview-cr / 469_3].

[0003] There are different methods for determining the GFR. They are most often classified into the following groups: measuring the GFR by the clearance of exogenously administered substances (exogenous markers of glomerular filtration), measuring the GFR by creatinine clearance (an endogenous marker of glomerular filtration), determining the GFR by performing a radionuclide study (dynamic nephroscintigraphy) and calculation methods based on determining the GFR using formulas [Baiko S.V., Kulakova E.N., Aksenova M.E. et al. Determination of glomerular filtration rate in children and adolescents: theoretical and practical aspects. Nephrology and dialysis. 2024; 26(2): 186-203. doi: 10.28996 / 2618-9801-2024-2-186-203].

[0004] A method for measuring SCF using the clearance of the following exogenous markers is known: inulin, iothalamate, iogexol, 99 mTc-DTPA, 51Cr-EDTA [Pottel H, Schwartz GJ. Measuring and estimating the GFR in children: state of the art in 2025. Pediatr Nephrol. 2025 Mar 11. doi: 10.1007 / s00467-025-06724-2. Epub ahead of print. PMID: 40067449]. The clearance of inulin, iothalamate, and iohexol is calculated after their intravenous administration and subsequent determination of concentrations in plasma and urine (renal / urinary clearance) or only in plasma (plasma clearance). After intravenous administration 99 mTc-DTPA or 51 Cr-EDTA measures the radioactivity of blood samples and determines the SCF based on the data obtained.

[0005] However, due to the invasiveness of the procedure, toxicity (including radioactivity) of the administered exogenous markers, their high cost, as well as the need for high-tech equipment, these methods are not available for widespread use and are not used in real clinical practice [Baiko S.V., Kulakova E.N., Aksenova M.E. et al. Determination of glomerular filtration rate in children and adolescents: theoretical and practical aspects. Nephrology and dialysis. 2024; 26(2): 186-203. doi: 10.28996 / 2618-9801-2024-2-186-203]. The scope of their application is limited to cases where other methods for determining GFR are uninformative, and the result of GFR measurement can have a significant impact on patient management tactics.

[0006] There is a method for determining the SCF using dynamic renal scintigraphy [Xie P, Huang JM, Liu X-M, Wu WJ, Pan LP, et al. (2013) 99mTc-DTPA Renal Dynamic Imaging Method May Be Unsuitable To Be Used as the Reference Method in Investigating the Validity of CDK-EPI Equation for Determining Glomerular Filtration Rate. PLoS ONE 8(5): e62328. doi: 10.1371 / journal.pone.0062328]. In this case, after intravenous administration 99 mTc-DTPA computes the GFR based on the image obtained without the need for blood samples. The method is based on recording the active accumulation of a labeled nephrotropic radiopharmaceutical (e.g., 99 mTc-DTPA) followed by determination of its excretion rate, which to some extent reflects the SCF.

[0007] The main disadvantage of this method is its low accuracy [Xie P, Huang JM, Liu H-M, Wu WJ, Pan LP, et al. (2013) 99mTc-DTPA Renal Dynamic Imaging Method May Be Unsuitable To Be Used as the Reference Method in Investigating the Validity of CDK-EPI Equation for Determining Glomerular Filtration Rate. PLoS ONE 8(5): e62328. doi: 10.1371 / journal.pone.0062328]. Therefore, international experts excluded this method from those recommended for determining GFR [Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int. 2024;105(4S):S117-S314].

[0008] There is a method for measuring GFR based on creatinine clearance (an endogenous marker of glomerular filtration) [Baiko S.V., Kulakova E.N., Aksenova M.E. et al. Determination of the glomerular filtration rate in children and adolescents: theoretical and practical aspects. Nephrology and dialysis. 2024; 26(2): 186-203. doi: 10.28996 / 2618-9801-2024-2-186-203]. During this study, a daily urine collection is performed (the child empties the bladder freely (without taking into account the amount of urine excreted) at 7:00 a.m.; after this, urine collection in one container begins throughout the day; at 7:00 a.m. the next day, the last urination is performed with urine collection in a container). Next, the volume of urine per day and the concentration of creatinine in the urine are determined. Blood sampling for serum creatinine measurement is performed on the day of urine collection. Endogenous creatinine clearance, which is equivalent to the SCF, is calculated using the following formula:

[0009] ,

[0010] where SCFcl is the endogenous creatinine clearance, ml / min / 1.73 m 2 ;

[0011] 1440 min - number of minutes in a day;

[0012] 1.73 m 2 - standard body surface area of ​​an adult;

[0013] The units of urine creatinine and serum creatinine should be the same (μmol / L or mg / dL).

[0014] This method was previously widely used in clinical practice. In recent years, its low accuracy has been established due to inaccuracies in 24-hour urine collection and the dependence of blood and urine creatinine on many factors unrelated to renal function. According to KDIGO experts, determining creatinine clearance from 24-hour urine collection remains acceptable, but only in cases where the SCF calculated using the formulas (see below) is considered insufficiently accurate for a particular patient, and measuring SCF using exogenous marker clearance is unavailable. In such clinical situations, patient training in 24-hour urine collection technique and / or external monitoring by parents and / or medical personnel are necessary.

[0015] There is a method for determining the estimated GFR (eGFR) based on serum creatinine levels using formulas. The most commonly used formula is the Schwartz bedside formula (CKiD). bed) [Clinical guidelines. Chronic kidney disease. Age category - children. Year of approval 2025. https: / / cr.minzdrav.gov.ru / preview-cr / 713_2] (Table 1).

[0016]

[0017] Despite the simplicity and accessibility of this method, it is characterized by insufficient accuracy in adolescents. Furthermore, there are significant differences in eGFR when switching at age 18 from the CKiDbed formula to the CKD-EPI formula, which is most commonly used in adults. In adolescents and young adults, the CKiDbed formula underestimates, while the CKD-EPI formula overestimates eGFR [Pottel H., , , et al. Estimating glomerular filtration rate at the transition from pediatric to adult care. Kidney Int. 2019; 95(5): 1234-1243. DOI: 10.1016 / j.kint.2018.12.020]. The average change in GFR when switching formulas can be up to +37 mL / min / 1.73 m 2[Kulakova E.N., Savchenko A.P., Nastausheva T.L., et al. Kidney diseases in adolescents classified according to the Kidney Disease and Function Nomenclature (KDIGO 2019): a cross-sectional study of the 2013-2022 regional registry. Nephrology and Dialysis. 2024; 26(3): 350-365. doi: 10.28996 / 2618-9801-2024-3-350-365]. These differences in the calculation of SCF are so significant that they lead to the definition of a different stage of CKD in young adults with the onset of the disease in childhood. This leads to a violation of the continuity of medical care and can have adverse consequences. A modification of the CKiDbed formula, the Schwartz-Leon formula, which is also noted in Russian clinical guidelines, does not solve this problem, also underestimating the GFR in adolescent patients [Baiko S.V., Kulakova E.N., Aksenova M.E. et al. Determination of the glomerular filtration rate in children and adolescents: theoretical and practical aspects. Nephrology and Dialysis. 2024; 26(2): 186-203. doi: 10.28996 / 2618-9801-2024-2-186-203].

[0018] In 2021, a new method for calculating SCF was proposed using the CKiD U25 formula for patients aged 1 to 25 years [Pierce S.V., , Ng DK et al. Age- and sex-dependent clinical equations to estimate glomerular filtration rates in children and young adults with chronic kidney disease. Kidney Int. 2021; 99(4): 948-956. doi: 10.1016 / j.kint.2020.10.047] (Table 2). This method was developed by the same group of researchers that developed the Schwartz bedside formula (CKiDbed).

[0019]

[0020] The purpose of developing the CKiD U25 formula was not only to improve the accuracy of calculating the SCF in children and adolescents with CKD, but also to solve the problem of inconsistency in determining the SCF in adolescents and young adults when switching at 18 years of age from calculating according to the CKiDbed formula to the CKD-EPI formula.

[0021] However, using the CKiD U25 formula instead of the CKiDbed formula reduces the differences in eGFR during the transition to CKD-EPI only in males (from 36.8 ml / min / 1.73 m 2 up to 19.4 ml / min / 1.73 m 2 ) [Kulakova E.N. CKiD U25 formula for calculating the glomerular filtration rate in adolescents. Russian Bulletin of Perinatology and Pediatrics 2025; 70:(4): 65-72. DOI: 10.21508 / 1027-4065-2025-70-4-65-72]. Thus, the updated formula also does not completely solve the problem of inconsistency in GFR calculations in pediatric and therapeutic practice.

[0022] There is a method to calculate GFR using the European Kidney Function Consortium (EKFC) formula [Pottel H., Bjork J., Courbebaisse M., et al. Development and validation of a modified Full Age Spectrum creatinine-based equation to estimate glomerular filtration rate: a cross-sectional analysis of pooled data. Ann Intern Med. 2021; 174(2): 183-191. DOI: 10.7326 / M20-4366] (Table 3).

[0023]

[0024] This method was supposed to completely solve the problem of changing formulas at certain age periods, as it is recommended by the developers from 2 to 100 years [Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int. 2024;105(4S):S117-S314].

[0025] However, this formula is used only in research practice. Its implementation in the healthcare system is predicted to significantly increase the number of adult patients with CKD, as the SCF calculation using the EKFC will be lower than that using the CKD-EPI formula. Furthermore, the EKFC requires software for use (and the availability of validated online calculators is currently limited). This formula also demonstrates lower accuracy compared to the CKiD U25 in children and adolescents with CKD and an SCF less than 75 ml / min / 1.73 m 2The height-dependent version of the formula has not been validated, which complicates its use in patients with developmental disabilities (short stature, tall stature). Given these limitations, the EKFC is recommended primarily for CKD screening, as well as for calculating SCF in healthy children and adolescents with SCF greater than 75 ml / min / 1.73 m 2 .

[0026] There are other formulas for calculating GFR in children and adolescents: for example, the FM formula, CKD-EPI 40 and LMR (Lund-Malmo Revised). These formulas have insufficient calculation accuracy compared to those presented above and are not widely used in either clinical or research practice [Kulakova E.N., Nastausheva T.L., Zvyagina T.G. et al. Problems of assessing glomerular filtration rate in adolescents and young adults: a descriptive review of the literature and examples from practice. Nephrology and Dialysis. 2021; 23(4): 472-488. doi: 10.28996 / 2618-9801-2021-4-472-488].

[0027] A common drawback of all formulas based on serum creatinine concentration is its dependence on many physiological and pathological conditions that lead to changes in blood creatinine levels but do not affect kidney function. The presence of such conditions in a patient will lead to incorrect results of the GFR calculation based on creatinine [Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int. 2024;105(4S):S117-S314]. For example, excessive muscle mass (athletes), overweight, and obesity are associated with higher creatinine concentrations regardless of actual kidney function and GFR. Protein-energy malnutrition (including as a result of nervous anorexia), neuromuscular diseases that occur with loss of muscle mass (myodystrophy, paraplegia, etc.) lead to a decrease in creatinine concentration.Consequently, in patients with excess muscle mass, the eGFR based on creatinine may be falsely decreased (i.e., a normal eGFR may lead to a result indicating decreased kidney function), while in patients with muscle mass deficiency, the eGFR based on creatinine may be falsely increased (for example, a falsely normal eGFR may be determined with decreased kidney function). A high-protein diet with a predominant content of animal protein, the use of certain medications (dexamethasone, trimethoprim, cimetidine, fenofibrate, certain antibacterial drugs, etc.), and comorbid conditions (sepsis, liver disease) can also affect serum creatinine concentrations without directly affecting renal function. Low SCF may lead to increased creatinine secretion in the renal tubules, which leads to a decrease in creatinine concentration and an overestimation of the eGFR (i.e., a calculated value higher than the true SCF).

[0028] There is a method for calculating GFR based on anthropometric (neck circumference), demographic (gender, age) data, and serum creatinine level [Patent JP 2020116100 A], but it was developed for adult patients. Improving the calculation of GFR using machine learning shows high potential, but is at the research stage and is not available for clinical practice. [Nakano, FK, , A., de Boer, J. et' al. Comparison between the EKFC-equation and machine learning models to predict Glomerular Filtration Rate. Sci Rep 14, 26383 (2024). https: / / doi.org / 10.1038 / s41598-024-77618-w].

[0029] Due to the listed shortcomings of creatinine (as a marker of glomerular filtration), a search for alternative markers is being conducted. The following substances were tested for the calculation of SCF: β2-microglobulin [Inker LA, Tighiouart H, Coresh J. et al. Estimation Using β-Trace Protein and β2-Microglobulin in CKD. Am J Kidney Dis. 2016 Jan;67(1):40-8. doi: 10.1053 / j.ajkd.2015.07.025.], sets of markers from the group (alanine, choline, creatine, dimethylsulfone, dimethylamine, glucose, glycerol, isoleucine, leucine, myo-inositol, N,N-dimethylglycine, valine) [WO 2020 / 065092], as well as other protein molecules [WO 2023278502], [WO 2015153860], [WO 2021132658]. However, the accuracy of calculating SFR using these markers remains lower than when using creatinine-based formulas, or they remain unavailable for clinical practice.

[0030] The closest technical solution to the proposed invention is the determination of SCF based on cystatin C. The concentration of cystatin C in the blood serum does not depend on muscle mass, gender, diet, but can change with the use of glucocorticosteroids, hypo- or hyperthyroidism, cytopenia, obesity, inflammation, smoking. The advantage of calculating the SCF based on cystatin C is the increased accuracy of the obtained value, as well as the reduction of differences when switching from pediatric (CKiD U25 ЦисС ) for therapeutic (CKD-EPI ЦисС ) formulas. This improves the continuity of medical care for adolescents and young adults.

[0031] The main method for determining the SCF in children and adolescents based on cystatin C is calculation using the CKiD U25 formula ЦисС(Table 4) [Baiko S.V., Kulakova E.N., Aksenova M.E. et al. Determination of glomerular filtration rate in children and adolescents: theoretical and practical aspects. Nephrology and Dialysis. 2024; 26(2): 186-203. doi: 10.28996 / 2618-9801-2024-2-186-203].

[0032]

[0033]

[0034] A disadvantage of the prototype is its limited availability in real-world clinical practice due to the lack of laboratory testing for cystatin C in many medical institutions. This is a technical issue that the proposed invention aims to address.

[0035] Disclosure of the invention. The technical result of the invention is the development of a method for determining the SCF in adolescents before transitioning to the adult healthcare system. This method improves the accuracy of the indicator and reduces the differences in SCF during the transition from pediatric to therapeutic calculation methods by using formulas based on cystatin C without laboratory determination.

[0036] The technical result is achieved by determining the serum creatinine of a 16-17 year old teenager in μmol / l, measuring his height in cm and body weight in kg, calculating his body mass index (BMI), determining the level of physical activity - strength training: yes or no, then determining the calculated level of cystatin C (pCystatin C), mg / l, according to the formula:

[0037]

[0038] in which the ratio of serum creatinine, μmol / L, to the patient's height, cm, is multiplied by the mandatory coefficient 2.2 and by additional coefficients under the following conditions: [*] multiplication by 1.1 is performed if the patient's BMI is less than 18.5, or the patient's BMI is greater than 25 in case of overweight / obesity; or the SCF according to the CKiD U25 formula based on creatinine determined in the patient's blood is less than 60 ml / min / 1.73 m 2 , [**] multiplication by 0.9 is performed during strength loads, then the resulting rCystatin C is used to determine the SCF using the formula CKiD U25 ЦисС :

[0039]

[0040] where k = 87.2 × 0.960( возраст-5 ) for males; k = 79.9 × 0.974( возраст-12 ) for females.

[0041] This method improves the accuracy of SCF determination in adolescents and reduces SCF differences during the transition from pediatric to therapeutic formulas, using the results of a publicly available laboratory test. A new feature of the proposed method is the determination of SCF based on calculated cystatin C. This expands the clinician's arsenal of options for determining SCF in adolescents before transitioning to the adult healthcare system.

[0042] When developing the presented method, the following sequence of actions was performed:

[0043] 1. In the first stage, a hypothesis was formulated that there is a relationship between the level of cystatin C and the level of creatinine in the blood serum, which can be described as a regression model that also includes the patient's anthropometric parameters and a number of coefficients.

[0044] 2. To test this hypothesis, an equation was compiled from two formulas for calculating the SCF (CKiD U25 ЦисС and CKiD U25 Kp) for teenagers 16-17 years old:

[0045]

[0046] 3. The following expression is obtained:

[0047]

[0048] where k is 1.87 for 17-year-old boys; 2.04 for 16-year-old boys; 1.96 for 17-year-old girls; 2.06 for 16-year-old girls. The average coefficient for 16-17-year-old adolescents, regardless of gender, was 2.0.

[0049] Testing and adaptation of the obtained equation were performed on a sample of 16-17 year old adolescents with CKD (30 patients).

[0050] 4. When calculating cystatin C using this formula and comparing the obtained result with the measured cystatin C, the following differences were revealed: the median (Me) was 0.13 mg / L, meaning the calculated value was lower than the measured value by an average of 13%.

[0051] In addition, the analysis of the obtained differences between the calculated and measured cystatin C allowed us to identify 3 groups of patients:

[0052] A. Patients whose calculated cystatin C level differed from the measured one by no more than 20%;

[0053] B. Patients whose calculated cystatin C was lower than the measured one by more than 20%;

[0054] C. Patients whose calculated cystatin C was higher than the measured one.

[0055] A qualitative analysis of the last two groups was performed. It was found that group B (calculated cystatin C lower than measured by more than 20%) included patients with malnutrition (SDS BMI less than -1; BMI less than 18.5), overweight / obesity (SDS BMI greater than 1; BMI greater than 25) and patients with SCF less than 60 ml / min / 1.73 m 2 Moreover, patients whose calculated cystatin C level was higher than the measured one differed from other adolescents in that they had engaged in intense strength training.

[0056] Consequently, the resulting formula systematically overestimated the desired indicator for the majority of patients and required further adaptation, including taking into account the selected groups.

[0057] 5. Based on regression analysis, it was confirmed that the creatinine-to-height ratio accounts for 99% of the variation in cystatin C levels in the study group. Therefore, the basic structure of the desired formula was left unchanged: multiplying the coefficient by the serum creatinine-to-height ratio.

[0058] Next, a regression analysis was conducted for the three groups specified above separately. The obtained coefficients were: for group A - 2.2; group B - 2.5; group C - 1.838. Thus, the differences in the coefficients between groups A and B, as well as A and C, amounted to 13%-16%. For practical use, the specified values ​​​​for groups B and C were transformed into additional (correction) coefficients to the main one (2.2), which was set for group A. For group B, the additional coefficient was 1.1; for group C - 0.9.

[0059] 8. The final formula was as follows:

[0060]

[0061] [*] Multiplication by 1.1 is performed if the creatinine concentration is below the level corresponding to the SCF (due to decreased muscle mass due to malnutrition (SDS BMI less than - 1; BMI less than 18.5), increased creatinine secretion with SCF less than 60 ml / min / 1.73 m 2 ), or predicted cystatin C concentration above the level corresponding to the SCF (due to overweight / obesity (SDS BMI greater than 1; BMI greater than 25)); [**] multiplication by 0.9 is performed if the creatinine concentration is above the level corresponding to the SCF (due to excess muscle mass and / or intense strength training).

[0062] When calculating cystatin C using the specified formula without taking into account additional coefficients and comparing the result with the measured cystatin C, a decrease in the difference was obtained (to 0.05 mg / L (Me)). Thus, the calculated cystatin C was lower than the measured one, but the difference decreased from 13% to 5.1% (Me).

[0063] When calculating cystatin C using the specified formula, taking into account additional coefficients, and comparing the result with the measured cystatin C, the difference decreased to -0.004 mg / L (Me). Thus, the calculated cystatin C was higher than the measured one, but with an average difference of 0.3%. However, no statistically significant differences were found between the calculated and measured cystatin C (p = 0.544).

[0064] Therefore, the calculated cystatin C can be used to determine the GFR using cystatin C-based formulas (CKiD U25 ЦисС , CKD-EPI ЦисС ), if there is no possibility of its laboratory determination.

[0065] This formula has limitations for use in the following cases: in adolescents with a transplanted kidney, acute kidney disease, including against the background of CKD, tubulopathies, during puberty (Tanner stage II-III), as well as in patients taking medications and having comorbid diseases, the effect of which on creatinine concentration is difficult to predict.

[0066] Brief description of the drawings. The invention is illustrated by a figure showing a block diagram of the method.

[0067] Embodiment of the invention. In a 16-17 year old adolescent, regardless of gender, the serum creatinine level (μmol / L) is determined by the enzymatic or Jaffe method with mandatory standardization according to IDMS (Isotope Dilution Mass Spectrometry). Height (cm) and body weight (kg) are measured using standard calibrated equipment. The body mass index (BMI) is determined (kg / m 2) and SDS BMI in accordance with the recommendations of the World Health Organization. The level of physical activity (intense strength training; yes / no) is clarified in the medical history. The calculated cystatin C level is determined using the proposed formula, taking into account additional coefficients for patients with malnutrition (SDS BMI less than -1; BMI less than 18.5), a decrease in SCF less than 60 ml / min / 1.73 m 2 , overweight, obesity, and intense strength training. The resulting calculated cystatin C level is used in the CKiD formula and25 ЦисС and others.

[0068] Internal validation of this method was performed by comparing the SCF determined from measured and calculated cystatin C levels (Table 5).

[0069]

[0070]

[0071] Thus, the comparison results did not reveal any statistically significant differences between the calculated and measured cystatin C, or between the SCF determined using formulas based on the calculated and measured cystatin C.

[0072] Next, the accuracy of determining the SCF based on creatinine and calculated cystatin C was assessed. The parameter - P was used as an accuracy assessment. 10 - the percentage of calculated SCF values ​​that were within ±10% of the available reference SCF value. The available reference value was the arithmetic mean of two SCF values ​​calculated using measured cystatin C and creatinine. According to published literature, this mean value is closest to the "gold standard" - SCF measured using exogenous markers. Higher P values 10(%) indicate a higher amount of SCF within ±10% of the reference value and, consequently, a higher accuracy of calculation using the analyzed formula (Table 6).

[0073]

[0074] The results show higher accuracy (P 10 ) in the SCF values ​​obtained on the basis of the calculated cystatin C level (CKiD U25 рЦисС ) compared with the value of SCF based on serum creatinine level (CKiD U25 Кр ). Thus, the use of calculated cystatin C brought the obtained result closer to the expected true level of SCF, that is, it increased the accuracy of SCF determination.

[0075] Next, a comparison of the SCF based on the calculated cystatin C level was performed using the pediatric (CKiD U25) and therapeutic (CKD-EPI) formulas (Table 7).

[0076]

[0077]

[0078] A smaller difference between the SCF according to CKiD U25 was obtained рЦисС and CKD-EPI pЦисС when using estimated cystatin C compared with the difference between the SCF according to CKiD U25 Кp and CKD-EPI Кp ) based on creatinine. This means that the use of calculated cystatin C allows for a reduction in the differences between pediatric and therapeutic formulas, thereby ensuring consistency in the provision of medical care to adolescents and young adults.

[0079] Below are examples of the use of the claimed method. The examples illustrate, but do not limit, the method.

[0080]

[0081]

[0082]

[0083]

[0084]

[0085] Thus, this method improves the accuracy of SCF determination in adolescents during the transition to the adult healthcare system and reduces discrepancies between SCF calculations using pediatric and therapeutic formulas. The method is technically simple, requires a minimal amount of sample material, is based on a readily available biochemical blood test, and can be used in clinical practice.

Claims

A method for determining the glomerular filtration rate (GFR) in adolescents aged 16-17 years with chronic kidney disease, including blood sampling, characterized in that in an adolescent aged 16-17 years, serum creatinine is determined, μmol / l, height is measured, body weight, kg, body mass index (BMI) is calculated, the level of physical activity is determined - strength loads: yes or no, then the calculated level of cystatin C (pCystatin C) is determined, mg / l, according to the formula: in which the ratio of serum creatinine, μmol / L, to the patient's height, cm, is multiplied by the mandatory coefficient of 2.2 and by additional coefficients under the following conditions: [*] multiplication by 1.1 is performed if the patient's BMI is less than 18.5, or the patient's BMI is greater than 25 in case of overweight / obesity; or the SCF according to the CKiD U25 formula based on creatinine determined in the patient's blood is less than 60 ml / min / 1.73 m 2, [**] multiplication by 0.9 is performed during strength loads, then the resulting rCystatin C is used to determine the SCF using the formula CKiD U25 ЦисС : where k=87.2×0.960 (возраст-15 ) for males; k=79.9×0.974 (возраст-12) for females.

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