Measured creatinine clearance compared to calculated creatinine clearance in hospitalized elderly males

Creatinine clearance is used as a measure of renal function and is useful for initiation and alteration of dosages of renally excreted drugs. Creatinine clearance approximates inulin clearance, which has been established as the most accurate measure of glomerular filtration rate. Determination of inulin clearance requires a constant plasma infusion of inulin and urinary tract catheterization, making this test a research tool with little practical application in the clinical setting. Ceatinine is an endogenous product of muscle metabolism, and unlike plasma urea levels, which vary depending on protein intake and changes in tissue catabolism, ceatinine excretion is fairly constant throughout a 24-hour period. The endogenous origin and constant plasma levels of creatinine afford a practical method for estimation of glomerular filtration, without the need for infusing an endogenous substance. Study objectives were: 1.) To determine which of five methods for estimation of creatinine fell within a range of +/- 20 percent of a 24-hour measured creatinine clearance; 2.) To determine the variation of estimating creatinine clearance by using actual body weight, ideal body weight or lean body mass. Subjects included in the study were males, 70 years of age or older, who were patients at the geriatric teaching and Evaluation Unit at the Salt Lake City Veterans Administration Medical Center from who informed consent was obtained.