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Prediction Equation for Glomerular Filtration Rate

TO THE EDITOR: Levey and colleagues (1) have provided an elegant prediction equation for the glomerular filtration rate (GFR) in patients with renal disease. It is, however, unlikely that busy practitioners who do not perform this calculation frequently will either remember or use it, especially when compared to the familiar, more user-friendly Cockcroft-Gault estimation. From a practical standpoint, a similar correction may be achieved while continuing to use the familiar Cockcroft-Gault formula: inserting the serum creatinine level obtained after the patient has ingested 2400 mg of cimetidine in three divided doses over 24 hours (2-4). A major cause of the approximately 20% overestimation of the GFR calculated from the creatinine clearance when the Cockcroft-Gault approximation is used is the increased contribution of tubular secretion of creatinine in patients with renal disease. Cimetidine can block tubular secretion of creatinine by competitively inhibiting cation transport in the luminal membrane of the proximal tubule (5). With this in mind, it would be of interest to know whether Levey and colleagues have compared their derived equation with the Cockcroft-Gault formula after cimetidine administration and whether the latter holds promise in day-to-day practice.