[Estimation of glomerular filtration rate in persons aged 69 years or older: agreement between distinct calculation methods].

Material: Estimation of glomerular filtration rate (eGFR) is the most widely accepted marker of renal function. Precise calculation is not routinely performed in clinical practice. Several methods have been developed for eGFR: creatinine clearance (CCr) calculation or the use of formulae derived from serum creatinine (sCr). The present study aimed to analyze the agreement between distinct methods of calculating eGFR.

Material And Methods: We performed a cross-sectional study between January and April, 2006 in 32 stable elders, aged 69 years or older, evaluated in a general nephrology unit. eGFR was calculated by CCr (considered the gold standard), Cockcroft-Gault (CG) and Modification of Renal Diet in Disease (MDRD) equations. The Mann Whitney U-test, Spearman's correlation coefficient and the Kappa coefficient were used to compare means and determine the concordance between methods.

Results: The overall means+/-SD of GFRe for CCr were 36.14+/-16 ml/min (range 11.75-69.6); CG: 37.02+/-16 ml/min (range 13.3-72.3) and MDRD: 45.52+/-16 ml/min (range 19.2-75.36). Variations in eGFR on comparison of methods were CCr and MDRD: -9.37 ml/min (95% CI:-13.85, -4.9); CCr and CG:-2.54 ml/min (95% CI: -6.95, 1.80); MDRD and CG: 9.0 ml/min (95% CI: 5.96, 12). The correlation between the gold standard (CCr) and sCr-derived formulae was r=0.74 for MDRD (P<0.001) and r=0.77 for CG (P<0.001). The Kappa value for CCr and CG was 0.44 and was 0.35 for CCr and MDRD. When patients were classified by stage of chronic renal disease, discrepancies were found according to the method used: stage 5 (eGFR<15 ml/min) was diagnosed in 13.63% with CG while none were diagnosed with stage 5 with MDRD.

Conclusions: In the estimation of the renal function in the elderly, eGFRe levels can differ in the same patient according to the method used: in view of the degree of concordance between CG and CCr, this mathematical formula should be used in preference to MDRD.