Comparison of cystatin C-based estimated glomerular filtration rate with measured glomerular filtration rate in a pediatric cohort of patients with chronic kidney disease.

Background: It is essential to have an accurate assessment of the renal function of patients with chronic kidney disease to monitor, treat, and predict further development of the condition. Measurement of renal function in terms of glomerular filtration rate (GFR) requires either urine or blood sampling, but especially in children, more simple methods of measurement are preferable. The main objective of this study was to examine if the estimated GFR (eGFR) calculated with different cystatin-C-based equations was comparable to the GFR measured by a radiotracer (mGFR) in pediatric patients.

Methods: In this retrospective study, 28 pediatric patients contributed with 73 pairs of measurements collected within 5 years. Bland-Altman Limits of Agreement were used to evaluate the performance and accuracy of two different cystatin-C-based estimates, the CKiD_Crea-CysC and the CKiD_U25 respectively, compared to an mGFR based on plasma clearance of technetium-99m-diethylenetriaminepentaacetic acid or chromium-51-ethylenediaminetetraacetic acid.

Results: Using the CKiD_Crea-CysC equation, 58.9% of the datasets were within P10 and 87.7% were within P30. The mean difference was 4.8 mL/min/1.73m² (standard deviation: 8.5 mL/min/1.73m²) and tended to overestimate GFR and thereby overrate the kidney function within the entire GFR range. Using the CKiD_U25 equation, 53.4% were within P10 and 93.2% within P30. The mean difference was -2.9 mL/min/1.73m² (standard deviation: 8.4 mL/min/1.73m²), but the difference varied with the GFR value.

Conclusions: A cystatin-C-based eGFR provides a viable substitute for monitoring renal function in pediatric patients with chronic kidney disease. However, it has a lower accuracy than mGFR and can therefore not replace mGFR in clinical use.