Estimation of glomerular filtration rate from serum creatinine and cystatin C in octogenarians and nonagenarians

BACKGROUND: Equations to estimate GFR have not been well validated in the elderly and may misclassify persons with chronic kidney disease (CKD). We measured GFR and compared the performance of the Modification of Diet in Renal Disease (MDRD), the Chronic Kidney Disease-Epidemiology Collaboration (CKD-Epi) and the Berlin Initiative Study (BIS) equations based on creatinine and/or cystatin C in octogenarians and nonagenarians. METHODS: Using cross-sectional analysis we assessed 95 very elderly persons (mean 85 years) living in the community. GFR was measured by iohexol (mGFR) and compared with estimates using six equations: MDRD, CKD-Epicreatinine, CKD-Epicystatin, CKD-Epicreatinine-cystatin, BIScreatinine and BIScreatinine-cystatin. RESULTS: Mean mGFR was 55 (range, 19-86) ml/min/1. 73 m (2). Bias was smaller with the CKD-Epicreatinine-cystatin and the CKD-Epicreatinine equations (-4. 0 and 1. 7 ml/min/1. 73 m (2) ). Accuracy (percentage of estimates within 30% of mGFR) was greater with the CKD-Epicreatinine-cystatin, BIScreatinine-cystatin and BIScreatinine equations (85%, 83% and 80%, respectively). Among the creatinine-based equations, the BIScreatinine had the greatest accuracy at mGFR < 60 ml/min/1. 73 m (2) and the CKD-Epicreatinine was superior at higher GFRs (79% and 90%, respectively). The CKD-Epicreatinine-cystatin, BIScreatinine-cystatin and CKD-Epicystatin equations yielded the greatest areas under the receiver operating characteristic curve at GFR threshold = 60 ml/min/1. 73 m 2 (0. 88, 0. 88 and 0. 87, respectively). In participants classified based on the BIScreatinine, CKD-Epicystatin, or BIScreatinine-cystatin equations, the CKD-Epicreatinine-cystatin equation tended to improve CKD classification (net reclassification index: 12. 7%, p = 0. 18; 6. 7%, p = 0. 38; and 15. 9%; p = 0. 08, respectively). CONCLUSIONS: GFR-estimating equations CKD-Epicreatinine-cystatin and BIScreatinine-cystatin showed better accuracy than other equations using creatinine or cystatin C alone in very elderly persons. The CKD-Epicreatinine-cystatin equation appears to be advantageous in CKD classification. If cystatin C is not available, both the BIScr equation and the CKD-Epicr equation could be used, although at mGFR < 60 ml/min/1. 73 m (2), the BIScr equation seems to be the best alternative.