Measurement of total bilirubin by use of bilirubin oxidase.

We used an enzymatic method for measuring total bilirubin in serum. Results by this method varied linearly with bilirubin concentrations to at least 300 mg/L. The day-to-day precision (CV) of the method ranged from less than 1% to about 11% at bilirubin concentrations of 183 and 12 mg/L, respectively. Commonly used anticoagulants, serum preparation materials, and selected drugs had no effect on the apparent bilirubin concentration, but turbidity caused a slight increase and hemoglobin concentrations of 2 g/L resulted in lower values, by as much as 17 mg/L at a bilirubin concentration of 95 mg/L. Patients' results obtained with this enzymatic method were slightly lower than those obtained with methods based on the Jendrassik-Grof principle. The largest differences, seen in samples with high "direct" bilirubin concentrations, can be decreased by measuring the absorbance at 425 nm instead of at 465 nm as recommended by the supplier of the bilirubin oxidase method.