Glomerular filtration rate-based cystatin C compared to microalbuminuria to detect early stage of diabetic nephropathy in children with type 1 diabetes mellitus

Microalbuminuria is a sensitive marker to detect early nephropathy in diabetes mellitus. Cystatin C correlates better than serum creatinine with microalbuminuria in type 1 diabetes mellitus (T1D). We evaluated the correlation between microalbuminuria, serum cystatin C (Cyc-C), and serum creatinine (SCr) in diabetic children. A hundred patients with stable T1D and 66 sex-matched healthy children were entered in the study between September 2008 and February 2011. Fasting blood sample was drawn for HbA₁C, creatinine, and cystatin C. A. 24-h urine aliquot was collected to measure microalbumin, creatinine, and volume. Glomerular filtration rate estimated based on creatinine (eGFR_cr), cystatin C (eGFR_{Cyst C}), and creatinine + cystatin C (eGFR_{Cyst C + Cr}). Binary logistic regression analysis, chi-square, ANOVA, Student’s t test, and nonparametric median tests were used to analyze data. P < 0.05 was considered significant. Medians serum creatinine and cystatin C of T1D group were significantly different from controls (P < 0.05). Overall, medians eGFR_{Cyst C} were higher than eGFR_cr, or eGFR_{Cyst C + Cr}. Thirty-six children with T1D had microalbuminuria. There was a correlation between microalbuminuria and eGFR_{Cyst C} (<60 and >130 ml/min/1.73 m²) (P < 0.05). Medians eGFR_cr were significantly lower than medians eGFR_{Cyst C} in T1D, regardless of microalbuminuria (P < 0.05). Chronic kidney disease classification according to eGFR_cr and eGFR_{Cyst C} were not matched (P < 0.05). GFR in healthy children was overestimated by eGFR_{Cyst C} and underestimated by eGFR_cr. There was higher correlation between abnormal eGFR_{Cyst C} and microalbuminuria in diabetic children. eGFR_Cr detected higher rate of GFR less than 60 ml/min/1.73 m².