Diagnostic Accuracies of Plasma Creatinine, Cystatin C, and Glomerular Filtration Rate Calculated by the Cockcroft–Gault and Levey (MDRD) Formulas

摘要

Estimation of the glomerular filtration rate (GFR) is the most widely used test of renal function, reflecting the relative mass of functional renal tissue and thus the number of functioning nephrons. Methods based on measurement of exogenous substances such as inulin, 51Cr-EDTA, 99mTc-diethylenetriaminepentaacetic acid, and iohexol are accurate but too complex and laborious for routine clinical use; thus, measurement of endogenous blood substances is common practice. Plasma or serum creatinine and its renal clearance are the approaches most commonly used despite their acknowledged unreliability.Cystatin C, a small basic protein, has been proposed as a better marker than creatinine. Recently, the value of cystatin C was thoroughly reviewed in this Journal (1), and according to this review and a new metaanalysis (2), most studies have concluded that cystatin C is superior to plasma creatinine, whereas several authors have concluded that cystatin C provides no advantage. One purpose of the present study was to clarify possible reasons for the earlier, partly conflicting results.A recently published guideline from the National Kidney Foundation (3) recommended that GFR be estimated from prediction equations taking into account the serum creatinine concentration and some or all of the following variables: age, gender, race, and body size. We therefore also compared cystatin C with GFRs calculated by the Cockcroft–Gault (4) and the MDRD(5) formulas.We studied 112 patients (55 men and 57 women) for whom 51Cr-EDTA clearance had been requested. The mean age of the patients was 57.0 years (range, 17–89 years). Body mass index (BMI) was 15.2–42.4 kg/m2, and 51 …