[Concordance between the equations "Chronic Kidney Disease Epidemiological Collaboration" and "Modification of Diet in Renal Disease" with the "Berlin Initiative Study" to estimate renal function in the elderly]

Abstract

Objective: Estimated glomerular filtration rate (eGFR) is calculated routinely using creatinine-based formulas, but their reliability in the elderly is limited. The aim of this study was to analyse the concordance between the BIS1 equation which is specific for the elderly, and the usual CKD-EPI and MDRD-IDMS in a large population over 70 years of age.

Material and methods: Retrospective cross-sectional study in which the eGFR was calculated using BIS1, CKD-EPI and MDRD-IDMS equations based on gender, age, and creatinine data of 85,089 subjects (58.5% women, mean age 78 years [IQR 73-83]).The following statistics were carried out: Wilcoxon test, Bland-Altman graphic analysis, study of the concordance using the intraclass correlation coefficient (ICC), and comparison tables for the classification of CKD.

Results: The median of the eGFRs using BIS1 was 58mL/min/1.73m² (IQR 48-70), using CKD-EPI was 68mL/min/1.73m² (IQR 53-84), and using MDRD it was 68mL/min/1.73m² (IQR 53-82). The concordance between BIS1 and CKD-EPI (intraclass correlation coefficient =0.87) was found to be acceptable. It was lower with MDRD (intraclass correlation coefficient =0.81). A mean difference of 8mL/min/1.73m² (SD 2.6-18) was found BIS1 vs. CKD-EPI, and 10mL/min/1.73m² (SD 6-27) with BIS1 vs. MDRD, which was maintained when stratifying by gender and age groups.

Conclusions: Despite the acceptable statistical agreement, the eGFR obtained with the BIS1 equation is not interchangeable with CKD-EPI or with MDRD-IDMS. The BIS1 equation gives lower values than CKD-EPI, and classifies patients into a higher level of CKD, mainly when the eGFR is above 30mL/min/1.73 m².

Keywords: BIS1 (Berlin Initiative Study); CKD-EPI; Chronic kidney disease; Enfermedad renal crónica; Estimated glomerular filtration rate; Filtrado glomerular estimado; MDRD-IDMS.