A quick and simple estimate of creatinine clearance

The 2 common estimates of renal function, the Cockcroft-Gault (C-G) and MDRD study equations, calculate glomerular filtration rate (GFR) as a function of serum creatinine. However, these equations require complex calculations and several parameters. We derived an equation to estimate creatinine clearance (eCCr) rapidly.

We studied 61 randomly selected patients. Our new formulae (eCCr) are eCCr (male) = weight/ creatinine; and eCCr (female) = weight x 0.84/creatinine (both with weight in kg). We compared eCCr to the long and short MDRD and C-G equations.

Agreement between the MDRD long and other formulae was determined using intraclass correlation (ICC); agreement with patient staging for estimated GFR <60 was done by kappa coefficient. ICCs were all >0.8, i.e., good overall agreement. ICCs were 0.96 for MDRD short, 0.84 for eCCr and 0.81 for C-G. Agreements for patients with GFR >60 were lower. MDRD short yielded the best agreement (kappa = 0.88; "good" agreement) followed by eCCr (kappa = 0.69; "fair" agreement) and C-G (0.56). ROC curve analysis showed an area under the curve (AUC) of 0.93, 0.98 and 0.90 for C-G, MDRD short and eCCr, respectively, as estimates of MDRD long (pe0.29). ROC curve analysis showed AUC=0.93 for MDRD short and 0.94 for eCCr as estimates of C-G (p=0.22).

We conclude that eCCr is a simple formula to estimate GFR at bedside, within a reasonable mathematical difference from the MDRD and C-G equations. This estimate can alert the physician to change drug dosing or more formally estimate GFR.