Glomerular filtration rate estimation in people older than 85: Comparison between CKD-EPI, MDRD-IDMS and BIS1...

The evidence of glomerular filtration rate (GFR) estimating with serum creatinine based formulae in the elderly population is scarce. The purpose of this study is to compare CKD-EPI, MRD4-IDMS and BIS1 equations to analyse correlation and concordance in a population older than 85 years old.

We designed a retrospective cross-sectional study, which included data from 600 patients older than 85 years. GFR was estimated by the following equations: CKD-EPI, MDR4-IDMS and BIS1, using as variables sex, age and serum creatinine concentration. Statistics analysis included Wilcoxon test, Bland-Altman plot, non-parametric Passing-Bablok method and kappa statistic (simple and weighted).

The patients' median (range) age was 87 (interval 85-98). The median GFR (range) was 42.4 (5.2-127.4) mL/min/1.73 m², when it was estimated with MDRD-IDMS, 40.0 (4.5-93.1) for CKD-EPI and 36.9 (7.6-83.7) for BIS1. The comparison of BIS1 and CKD-EPI and MDRD-IDMS using the Wilcoxon test was significant (P<.001). The regression analysis yielded the following equations: MDRD-IDMS= 1,025×CKD-EPI+1.360; BIS1= 0.688×CKD-EPI+9.074 and BIS1= 0.666×MDRD-IDMS+8.401. The weighted coefficient was 0.958 for the concordance between MDRD-IDMS and CKD-EPI, 0.812 for the concordance between MDRD-IDMS and BIS1 and 0.846 for CKD-EPI and BIS1.

The GFR estimations obtained with BS1 equation are not interchangeable with MDRD-IDMS or CKD-EPI equations. BIS1 estimates lower GFR values than MDRD-IDMS and CKD-EPI and tends to classify the patients in a more advanced chronic kidney disease stage, especially for estimated GFR higher than 29mL/min/1.73 m².