Serum cystatin C as a reliable marker of changes in glomerular filtration rate in children with urinary tract malformations

PURPOSE: Cystatin C has been suggested as a simple method of estimating GFR more accurately than creatinine in children. We compared the diagnostic accuracy of cystatin C with serum creatinine and the Schwartz formula for estimating GFR in patients with UTMs. MATERIALS AND METHODS: We prospectively compared 72 patients with UTMs (20 days to 36 months old, 58 males and 14 females) with a group of 72 healthy controls (10 days to 48 months old, 53 males and 19 females). All patients underwent nuclear medicine clearance investigations with (99m)Tc DTPA. RESULTS: Serum concentration of cystatin C revealed a higher correlation with (99m)Tc DTPA (r = 0.62, p <0.001) than serum concentration of creatinine (r = 0.30, p <0.01) or Schwartz formula (r = 0.51, p <0.001). These results were more evident in patients with uropathy (19) with mild renal impairment. Agreement between methods was assessed using Bland Altman analysis. Mean differences between GFR calculated with (99m)Tc DTPA and cystatin C based GFR estimation or Schwartz formula were -2.6% +/- 46.7% and -73.4% +/- 53.6%, respectively. Diagnostic accuracy in identifying decreased GFR measured as AUC was always highest for cystatin C but hardly sufficient for the 3 variables. Cystatin C performed better in the 0 to 6-month-olds (0.70 +/- 0.08 for cystatin C, 0.58 +/- 0.07 for Schwartz estimate) and patients older than 12 months (0.82 +/- 0.09 for cystatin C, 0.65 +/- 0.11 for Schwartz estimate). CONCLUSIONS: Cystatin C proved to be a superior marker rate over serum creatinine in estimating glomerular filtration in children younger than 3 years with UTMs and mild renal impairment, thus, offering a more specific and practical measure for monitoring GFR.