I describe a semi-micro method for use with a discrete analyzer, the Abbott ABA-100, requiring 75 microliter of sample for determination of both the total and direct bilirubins. This method utilizes a serum blank. It is simple and reasonably rapid. The azobilirubin formed by both the total and the direct bilirubins produces a reddish-violet color, which is measured at 550 nm. Values obtained are comparable to those by the automated Jendrassik and Grof procedure adapted by Gambino and Schreiber (total r = 0.999, direct r = 0.990). The method is linear to 300 mg/liter. Day-to-day precision (CV) for the total bilirubin was 8.8% for a 8 mg/liter sample (n = 45) and 4.7% for a 57 mg/liter sample (n = 46). The absorbance of hemoglobin and its derivatives (540 nm) caused a false decrease in the measured bilirubin content, the direct being more affected than the total. This problem was alleviated by the use of caffeine and acid blanks.
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L Mori (1978) studied this question.