Performance of creatinine-based equations compared in older patients

The current equations for estimating glomerular filtration rate (GFR) have limited precision in older people. The Berlin Initiative Study (BIS-1) equation has recently been developed to improve the precision and accuracy of GFR estimation in older people, over the previous simplified Modification of Diet in Renal Disease (MDRD) Study and the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations.

The study included 224 white patients aged >70 years who had simultaneous measurements of plasma creatinine and renal clearance of inulin. Creatinine assays used an enzymatic method with calibrators defined by isotope dilution mass spectrometry. The performance of BIS-1, MDRD and CKD-EPI equations in estimating GFR were compared.

BIS-1 was the most accurate: the percentage of GFR estimates that fell within the range of measured GFR ± 30% (P30) was 75.56% vs. 70.67% with MDRD and 72% with CKD-EPI. BIS-1 had the lowest median bias: (interquartile range) (4.1 (11.4) vs 5.8 (12.7) and 5.4 (12.8) respectively) the highest precision (the SD of the estimated GFR minus measured GFR differences was 9.21 vs 12.78 and 10.83 mL/min/1.73 m² respectively) and the highest concordance correlation coefficient (CCC) (0.82 vs. 0.74 and 0.79 respectively, p<0.05). However, in chronic kidney disease (CKD) stages 4 and 5, the CKD-EPI equation had the highest P30, the lowest median bias and the highest CCC: it was more accurate than the BIS-1 equation.

Among the 3 creatinine-based equations compared, BIS-1 was the most reliable for assessing renal function in older white patients, especially in those with CKD stages 1 to 3.