EGFR

Abstract

GFR is the accepted metric for evaluating renal function but measuring it directly (mGFR) can be cumbersome, time-consuming, and costly. The constant infusion method using inulin as the filtration marker, introduced in 1934 by Richards and Smith (1), has undergone many revisions that have now made mGFR easier to perform, although not widely available (2,3). A simple, reliable, unbiased, precise, and accurate estimation of mGFR, without reliance on constant infusions or timed urinary collections, would be welcome; however, as illustrated by the extensive compendium of comparisons of mGFR (using classical inulin clearance methods) to eGFR by Botev et al. (4) in this issue of CJASN , this objective is far from being realized. Although formulaic methods to approximate the values of mGFR from serum creatinine (Scr) levels have been used for many decades, the seminal description of the Modification of Diet in Renal Disease (MDRD) equation (eGFR-MDRD) in 1999 galvanized interest in this common and important clinical issue (5). The often used Cockcroft-Gault equation (6) was never intended to be an approximation of GFR but rather was designed to estimate endogenous creatinine clearance, which is not equivalent to GFR because of the effects of tubular secretion of creatinine (TScr). In normal individuals, this can be compensated for by a correction factor, because TScr is relatively constant (at approximately 22 to 24% of GFR) (7); however, TScr can vary markedly in disease states, particularly those associated with heavy proteinuria (8). Compared with mGFR, the current widely used eGFR-MDRD formulas (original and reexpressed [5,9]) have limitations because of variable degrees of bias, imprecision, and inaccuracy (10). The studies of Botev et al. (4) in this issue of CJASN provide additional quantitative data on the ranges of bias, precision, and accuracy of eGFR-MDRD according to the levels …