A peroxidase-coupled kinetic enzymatic procedure evaluated for measuring serum and urinary creatinine

We evaluated an enzymatic procedure for the automated determination of serum and urinary creatinine. The procedure was sensitive and precise for serum creatinine concentrations as low as 3 mg/L, and the standard curve was linear to 200 mg/L. Measurements of creatinine in clinical serum and urine specimens agreed with those obtained by two other enzymatic methods and four picric acid methods. There was no interference from picrate-reactive substances tested. Among other substances, bilirubin (50-100 mg/L) interfered negatively with the assay, decreasing apparent creatinine concentrations by as much as 6 mg/L. The advantages of specificity, speed, and convenience make this enzymatic procedure an attractive primary or secondary method for creatinine determinations in clinical laboratories.