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 μL of serum or 3 μL 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 μmol/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 μmol/L (6·2–10·9 mg/L) in men and 40–66 μmol/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.