Cystatin-C outperforms creatinine for estimating renal function in adolescents with anorexia nervosa: cross-sectional method-comparison study

Individuals with anorexia nervosa are at increased risk of renal impairment, but assessing renal function in this population remains challenging. Cystatin-C, which is less affected by nutritional status than creatinine, may provide a more reliable biomarker. However, equations based on cystatin-C (CKiD‑U25, EKFC, and CKD-EPI) have not yet been evaluated against isotopic scintigraphy in individuals with anorexia nervosa. This study aimed to compare the performance of creatinine-based and cystatin-C-based equations (CKiD-U25, EKFC, CKD-EPI) against 99mTc-DTPA renal scintigraphy as the reference standard in adolescents with restrictive anorexia nervosa. Glomerular filtration rate was measured using renal scintigraphy and estimated with creatinine-based and cystatin-C-based equations. Serum cystatin-C and creatinine were measured at hospital admission (day 0), whereas renal scintigraphy was performed as soon as feasible after admission (mean of 5 days), in adolescents with restrictive anorexia nervosa. Correlation coefficients, mean bias, root mean square error, and Bland–Altman plots were assessed. Across all equations, cystatin-C-based formulas consistently outperformed creatinine-based ones in terms of correlation, bias, and precision. The CKiD-U25 using cystatin-C equation showed the strongest correlation with renal scintigraphy (r = 0.77; bias = – 11.5 mL/min/1.73 m2). At admission for restrictive anorexia nervosa, cystatin-C-based equations, particularly the CKiD-U25, demonstrate superior agreement with renal scintigraphy compared to creatinine-based equations, making cystatin-C-based equations more reliable in this context. Individuals with anorexia nervosa are at higher risk for renal problems, but it can be difficult to measure how well their kidneys are functioning. The most common test uses a blood marker called creatinine, which depends on muscle mass and protein intake. Another blood marker, called cystatin-C, is not affected by muscle mass loss and or protein intake and may provide a more accurate result. In this study, we compared several methods of estimating renal function in adolescents hospitalized for anorexia nervosa. We found that equations using cystatin-C were more reliable than those using creatinine. Among these, the CKiD-U25 formula proved to be the most effective. Our results suggest that formulas using cystatin-C could be useful for estimating renal function in adolescents hospitalized for anorexia nervosa.