Increased urinary cystatin C reflects structural and functional renal tubular impairment independent of glomerular filtration rate

Objectives: The ratio of the urinary mass concentrations of cystatin C and creatinine (UcysC/Ucrea)>= 11.3 mg/mmol has recently been proposed as an accurate marker for the detection of GFR <= 60 mL/min/1.73 m(2). Design and methods: We prospectively evaluated the diagnostic performance of UcysC/Ucrea >= 11.3 mg/mmol and factors associated with increased UcysC/Ucrea in 72 children and adults with a wide variety of renal disorders. UcysC/Ucrea was calculated, and GFR wad estimated from serum creatinine and cystatin C by equations. Results: UcysC/Ucrea >= 11.3 mg/mmol had a low diagnostic value to detect GFR values <= 60 mL/min/1.73 m(2) estimated by creatinine or cystatin-C-based equations with sensitivities of 72% and 63%, and specificities of 42% and 34%. ROC curves for UcysC/Ucrea to detect GFR: 60 mL/min/1.73 in 2 confirmed this with AUCs of 0.59 for creatinine and 0.57 for eystatin-C-based equations. Multivariate analysis identified tubular proteinuria, tubutointerstitial disease and heavy proteinuria, but not GFR <= 60 mL/min/1.73 m(2), as factors independently associated with increased UcysC/Ucrea. Conclusions: UcysC/Ucrea >= 11.3 mg/mmol is not an accurate marker to detect GFR <= 60 mL/min/1.73 m(2), but reflects tubular dysfunction and proteinuria due to heavy proteinuria and tubulointerstitial disease. (c) 2007 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.