The laboratory method as a variable in the interpretation of serum bilirubin fractionation

Fractionation of the serum bilirubin into direct and indirect-reacting components has been used in the differentiation of patients with hepatobiliary disease from those with unconjugated hyperbilirubinemia. Previous studies have shown that patients with indirect hyperbilirubinemia usually have total serum bilirubin concentrations less than 5 mg/dl. Therefore, clinically useful methods of fractionating bilirubin must yield reliable results in patients with mild hyperbilirubinemia. Experience with 4 patients with mild hyperbilirubinemia indicated that conflicting results could be obtained from two different laboratories. Therefore, a panel of hyperbilirubinemic sera were submitted to four different laboratories. While there was general agreement in sera containing high concentrations of bilirubin, marked variations were observed in the results reported on sera with less than 5 mg/dl total bilirubin. Finally, clinical and other laboratory parameters were reviewed in patients who had had bilirubin fractionation performed by one or the other of two routine laboratories. In one laboratory, bilirubin fractionation correctly distinguished patients with hepatobiliary disease, while the other laboratory was not able to differentiate patients on the basis of this test. These data suggest that despite the general reported agreement in standard methods for bilirubin fractionation there may be marked differences among methods in ability to reliably fractionate sera with total bilirubin concentrations less than 5 mg/dl.