Development of an equation to correct for hemolysis in direct bilirubin measurements

Background: Direct bilirubin is measured for the investigation of pediatric and adult jaundice. Package inserts suggest that hemolysis decreases direct bilirubin measurements, but no published studies have adequately described the extent of interference.

Methods: The influence of hemolysis on direct bilirubin quantification (Beckman AU680) was evaluated by titrating increasing amounts of hemoglobin into specimens with variable starting concentrations of direct bilirubin. An equation was derived to predict the nominal interference-free concentration of direct bilirubin as a function of measured concentration and hemolysis-index.

Results: Hemolysis decreased the direct bilirubin concentration reported by the AU680. The extent of interference is a function of both the interference-free concentration of direct bilirubin and the degree of hemolysis.

Conclusions: The concentration of direct bilirubin in hemolyzed specimens can be predicted.