Comparison of Jaffé rate assay and enzymatic method for the measurement of creatinine clearance.

To evaluate the relationship between Jaffé rate assay (Jaffé assay) and creatinine amidohydrolase enzymatic method (enzymatic method), we measured serum and urine creatinine concentrations in 100 serum and 100 urine samples by two methods in patients with renal disease. Comparison of Jaffé (X) and enzymatic (Y) measurements of serum and urine creatinine levels revealed a high correlation (r2 = 0.9991 in serum, r2 = 0.9995 in urine). The creatinine concentrations in serum and urine determined by Jaffé assay were significantly (p < 0.01) higher than those assayed by the enzymatic method. The relationship between Jaffé and enzymatic analyses of creatinine clearance (Ccr) was obtained mathematically using regression lines (Y = 0.977X - 0.199 in serum, Y = 0.999X - 1.872 in urine). Ccr values obtained by both methods were almost the same at high serum creatinine levels. However, Ccr determined by Jaffé assay was much lower than that obtained by the enzymatic method when the serum creatinine concentration was under 2.0 mg/dl. We present here the equation for conversion of clearance values determined by both methods to obtain an accurate evaluation of renal function in many clinical studies.