CKiD U25 equation for calculating glomerular filtration rate in adolescents

The KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease presents three validated equations for estimating glomerular filtration rate in children and adolescents: CKiD U25, EFKC, and CKD-EPI40. Study objective. Determine the clinical significance of using the CKiD U25 equation instead of the Bedside Schwartz equation to calculate glomerular filtration rate in adolescents.

Materials and methods. Single-center, cross-sectional study based on a 10–year regional register of 17–year-olds. Glomerular filtration rate was calculated using the Bedside Schwartz, CKiD U25 and CKD-EPI equations.

Results. Calculating glomerular filtration rate for 17–year-olds using the CKiD U25 and Bedside Schwartz equations yielded the following results: 94 [81.5; 107] and 85 [75; 99] ml/min/1.73 m², respectively. The median of differences was +16.3 ml/min/1.73 m² for males and —0.7 ml/min/1.73 m² for females. These differences resulted in a change in the glomerular filtration rate category for 44.7% (208/465) boys and 2.6% (11/428) girls. Using the CKiD U25 equation decreased estimated glomerular filtration rate differences during the switch to CKD-EPI in males from 36.8 to 19.4 ml/min/1.73 m² and increased them in females from 21.9 to 22.95 ml/min/1.73 m². When switching from the Bedside Schwartz equation to the CKD-EPI equation at the age of 18, the glomerular filtration rate category changed for 55.8% (498/893) patients; from the CKiD U25 equation to the CKD-EPI equation for 33.9% (303/893) patients. Comparison of glomerular filtration rate based on CKiD U25 and CKD-EPI equations at age 25 years revealed differences in the glomerular filtration rate category in 25.8% (230/893) of patients.

Conclusions. Using the CKiD U25 equation instead of the Bedside Schwartz equation in 17–year-olds leads to a clinically significant change in estimated glomerular filtration rate only in males. The advantage of this equation is that it reduces the risk of misclassification of glomerular filtration rate category (G1–G5) for patients transitioning to an adult healthcare system that uses the CKD-EPI equation.

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