External validation of the Berlin equations for estimation of GFR in the elderly.

Chronic kidney disease prevalence increases markedly with age1 and accurate estimation of GFR is an important issue in older people. The Chronic Kidney Disease Epidemiology Collaboration creatinine equation (CKD-EPIcr)2 and variations including cystatin C (CKD-EPIcys) or both creatinine and cystatin C (CKD-EPIcr-cys)3 have been recommended for estimating GFR.4 Recently, the Berlin Initiative Study (BIS) reported 2 GFR equations specifically developed in older people: BIS1, which uses creatinine, and BIS2, which uses both creatinine and cystatin C.5 Here, we compare how the BIS and CKD-EPI equations perform in a large cohort of older people.