GFR estimates using cystatin C are superior to serum creatinine in adult patients with cystic fibrosis

Abstract 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 m2 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 m2. Conclusion Cystatin C clearance provides an improved marker of glomerular filtration rate in CF patients.