RESUMEN
BACKGROUND: Accurate assessment of renal function in patients with cystic fibrosis (CF) is vital for determining the appropriate dose of medications and for early detection of renal disease. Cystatin C (CysC) is a new marker of GFR with reportedly improved accuracy and precision compared to methods incorporating serum creatinine. The purpose of this study is to evaluate the predictive performance of cystatin C in estimating GFR in adult patients with CF. METHODS: Iothalamate was administered to enable measurement of GFR in 38 adult patients with CF and control subjects. Creatinine clearance (C&G) and GFR estimates (cystatin C clearance [Cys C] and abbreviated modified diet in renal disease [aMDRD]) were compared using Bland-Altman and receiver operating characteristic (ROC) analysis. GFR cutoff values of 80 and 90 mL/min-1.73 m(2) were used in the analysis. RESULTS: The measured GFR was similar in both the CF and healthy volunteers 104 (32.2) and 105 (29.9), P=0.969 respectively. No significant difference in mean bias was noted between the predictive methods within the CF population. Cys C provided the most precise estimates of GFR in both populations. ROC curves demonstrated that CysC provided greater sensitivity and specificity compared to the aMDRD (AUC 0.93 vs. 0.54, P=0.003) and C&G (AUC 0.93 vs. 0.56, P=0.005) in CF at a cutoff GFR of 90 mL/min-1.73 m(2). CONCLUSION: Cystatin C clearance provides an improved marker of glomerular filtration rate in CF patients.