Individual determination of glomerular filtration rate from plasma creatinine

A method for calculating glomerular filtration rate (GFR) in the individual patient from plasma creatinine concentration only is presented. By this method the urinary excretion rate of creatinine (u) in the individual patient is determined indirectly from a simultaneous determination of GFR (measured without urine collection from the total [51Cr]EDTA plasma clearance) and plasma concentration of creatinine (p) according to the equation u =p(0.968GFR + 4.11), in which the expression in parentheses corresponds to the regression of endogenous creatinine clearance on GFR as determined in 67 patients, covering a wide range of renal function. Hereafter (as long as u is constant), GFR in the individual patient is calculated solely from any new determination of p according to the equation GFR = (u/p-4.11)/0.968. The reliability of the method was confirmed by the finding of a close correspondence between the values of calculated GFR and measured GFR in 6 patients with rapid changes in renal function and in 14 patients investigated twice with a time interval of 5-18 months. The practical application of the method by a nomogram is presented elsewhere in this issue of the journal.