Detection and measurement of total bilirubin in serum, with use of surfactants as solubilizing agents.

We describe a new method for measuring total bilirubin in serum. Nonionic, cationic, or anionic surfactants can be used as solubilizing agents to promote the diazo coupling of indirect-reacting bilirubin. A representative surfactant-azobilirubin system is illustrated, in which absorbance is maximum at 560 nm and linear to a concentration of 200 mg of bilirubin per liter. At pH 2.5 and in the presence of Duponol (an anionic surfactant), bilirubin is completely coupled within 6 mm at 37 #{176}C. All ingredients required for an assay are combined in two dry reagents, which are stable for a year at room temperature. Sensitivity is comparable to that of procedures routinely used in clinical laboratories; precision, linearity, and stability of the reagents in solution are excellent. Results for fresh sera correlated well with those obtained by the Jendrassik-Grof method. Hemolysis is minimized and turbidity eliminated.