Prediction of creatinine clearance from serum creatinine in patients with rheumatoid arthritis: comparison of six formulae and one nomogram

The estimation of glomerular filtration rate is important for the medical treatment of patients with rheumatoid arthritis (RA). However, the determination of endogenous creatinine clearance (Clcr) from a 24-h urine collection is an unreliable and time-consuming procedure. We therefore tested the accuracy of six equations and one nomogram for the prediction of Clcr from serum creatinine (Scr) in 38 patients with RA and 20 controls. A positive correlation was found for all methods in the controls (r = 0.83-0.94) and RA patients (r = 0.51-0.69). The methods did not overestimate Clcr in RA. In the RA group the simple formula published by Cockcroft [Clcr = ((140 - age) x body weight)/(72 x Scr), x 0.85 for females] showed the best correlation with the measured Clcr. In RA the Cockroft formula can reliably be used to predict Clcr from Scr.