Performance of GFR Estimation in Finnish Children and Adolescents

Introduction 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). Methods Our study included patients under 20 years of age 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 them, and compared with mGFR in terms of bias, precision and accuracy. Results Our cohort consisted of 516 patients aged 0.8─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 IFCC reference material, the CKiD (2012) combination equation had the lowest median bias (0.1 ml/min/1.73m 2 ), IQR (14.6 ml/min/1.73m 2 ) and the highest P 10 and P 30 accuracies (47.3% and 94.6%). It also surpassed the P 30 threshold of 90% in all age groups. Other combination equations showed similar median bias (between 2.6 to 4.0 ml/min/1.73m 2 ) and P 30 accuracy (between 86.4% and 90.1%), with overlapping 95% confidence intervals. Conclusion 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.