[Is fractionation of serum bilirubin useless?]

The validity of fractionation of serum bilirubin into direct and indirect fractions for differentiation of haemolytic and hepatobiliary hyperbilirubinaemia was assessed in 20 patients with haemolysis and 72 patients with hepatobiliary diseases. The groups varied significantly regarding the ratio of direct and total bilirubin (0.45 +/- 0.24 vs. 0.58 +/- 0.18, P less than 0.005). Due to the frequency distribution between both groups in each patient there was an a-priori probability of haemolysis of 22% and of hepatobiliary disease of 78%. Fractionation increased the probability of correct diagnosis from 22% to 55% and from 78% to 91%. Exclusion of patients with a total bilirubin of more than 3 mg/dl (51 mumol/l) increased the probability from 26% to 80% and from 74% to 86%. Thus fractionation of serum bilirubin is a considerable gain for the diagnosis of haemolysis, particularly in relatively low total bilirubin. The more frequent hepatobiliary diseases can be better diagnosed using other laboratory methods. Thus fractionation is useful only when a hepatobiliary disease has been established as unlikely beforehand.