Reference values of serum and urine creatinine, and of creatinine clearance by a new enzymatic method

A new, totally enzymatic procedure for the determination of creatinine in serum and urine, using creatinine amidohydrolase, creatine amidinohydrolase, sarcosine oxidase and formaldehyde dehydrogenase is described. The assay was adapted to a discontinuous analyser with each analysis requiring only 20 microL of serum or 3 microL of urine. Analytical recovery of creatinine in serum and urine averaged 100.6%. Within-run and between-run precision studies gave coefficients of variation of 1.1% and 1.8%, respectively, for a serum with mean values of 83 mumol/L (9.4 mg/L) creatinine. Creatinine concentrations in serum and urine were measured by this procedure, in Japanese children and adults. The reference intervals for serum creatinine concentrations in adults were 55-96 mumol/L (6.2-10.9 mg/L) in men and 40-66 mumol/L (4.5-7.5 mg/L) in women, and for urine, 9.46-19.01 mmol/day (1070-2150 mg/day) in men and 6.75-10.61 mmol/day (764-1200 mg/day) in women. The reference intervals of creatinine clearance were 88.0-176.4 mL/min in men and 75.7-173.0 mL/min in women.