Measurement of bilirubin by HPLC in bovine plasma--a comparison with the conventional diazo-method

Application of a HPLC-technique according to MURACA & BLANCKAERT (1983) for accurate determination of the relative amounts of unconjugated bilirubin and its sugar mono- and diconjugates in bovine plasma is described and the results are compared with those of the conventional diazo-method. The diazo-assay yielded values for total and unconjugated bilirubin which were considerably higher than those obtained by the HPLC-technique. This is probably due to unidentified diazo-positive compounds distinct from bilirubin. The direct-reacting fraction in the diazo-assay showed little or no agreement with the fraction of total ester conjugates determined by HPLC. Results indicate that the diagnostical value of bilirubin subfractioning by the diazo-method as a liver function test in cattle must be reconsidered.