Estimation of Glomerular Filtration Rate by Using Serum Cystatin C and Serum Creatinine Concentrations in Patients with Human Immunodeficiency Virus

Study Objective. To compare the predictive performance of four equations for estimating glomerular filtration rate (GFR) relative to the gold standard measurement, iothalamate clearance, in patients-with human immunodeficiency virus (HIV) who have various degrees of kidney function. Design. Prospective, cross-sectional analysis. Setting. General clinical research center. Patients. Twenty-two adult (mean age 51 yrs) HIV-positive patients with various degrees of stable kidney function and with lean body mass considered normal for a well-nourished person. Intervention. Patients were administered a single dose of intravenous iothalamate 456 mg as a rapid infusion over 3 minutes, 1 hour after an oral fluid load of 600 ml of caffeine-free, sugar-free liquids. Measurements and Main Results. Serial blood and urine samples were obtained for determination of measured GFR. Estimated GFR values were calculated by using four equations: the Cockcroft-Gault equation, the simplified Modification of Diet in Renal Disease Study (MDRD) equation, an equation that incorporates serum creatinine and cystatin C concentrations, and an equation incorporating only serum cystatin C concentration. The predictive performance of the equations was determined by comparing the bias, accuracy, and precision of the estimates with the measured values. Body composition was determined by dual-energy x-ray absorptiometry. The four predictive equations underestimated the measured GFR obtained by the iothalamate method, but the differences were not statistically significant. The MDRD equation and the equation that included both serum cystatin C and creatinine concentrations, as well as age, sex, and race, provided the least bias, most precision, and best accuracy in estimating the measured GFR. Conclusion. The MDRD equation and the equation that included both serum cystatin C and creatinine concentrations appear to provide accurate, precise, and relatively unbiased estimates of GFR in patients with HIV Larger studies are needed that include patients with muscle wasting and lipodystrophy in order to validate these preliminary observations and the effects of body composition on the predictability of GFR with use of these equations.