Performance of GFR Estimation in Finnish Children and Adolescents

The accuracy of estimating glomerular filtration rate (GFR) using endogenous biomarkers has been widely studied, and many GFR estimating equations have been proposed. In this study, we compared the performance of these equations in a Finnish population and evaluated their accuracy in different age groups and categories based on measured GFR (mGFR).

Our study included patients under the age of 20 years whose GFR was measured between September 2014 and April 2025. Patient information was collected retrospectively from the Helsinki University Hospital electronic data lake. GFR was estimated with multiple equations, using either a single analyte or a combination of analytes, and was compared with mGFR in terms of bias, precision, and accuracy.

Our cohort consisted of 516 patients aged from 0.8 to 19.9 years with a history of solid organ transplantation, malignancy, or suspected kidney impairment. In general, creatinine-cystatin C-based combination equations exhibited better performance than single-analyte equations. Despite developed using cystatin C not calibrated to International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) reference material, the Chronic Kidney Disease in Children (CKiD) (2012) combination equation had the lowest median bias (0.1 ml/min per 1.73 m²), interquartile range (IQR; 14.6 ml/min per 1.73 m²), and the highest P₁₀ and P₃₀ accuracies (47.3% and 94.6%, respectively). Moreover, it surpassed the P₃₀ threshold of 90% in all age groups. Other combination equations showed similar median bias (between 2.6 and 4.0 ml/min per 1.73 m²) and P₃₀ accuracy (between 86.4% and 90.1%), with overlapping 95% confidence intervals (CIs).

Combination equations provided more accurate estimates of GFR than single-analyte equations. Selected combination equations accurately estimated GFR across all age groups, a finding that is likely population dependent.