Determination of serum bilirubin by the diazo method using the diazotized 3-nitroaniline reacting readily with the photoproducts of bilirubin

Summaru We studied the diazo reaction of the water-soluble photoproducts of bilirubin using nine kinds of diazonium salts to select the diazonium salt most suitable for the determination of serum bilirubin. The diazonium salt of 3-nitroaniline was found to be more suitable than that of sulfanilic acid used extensively in clinical practice. This diazonium salt reacted readily with not only bilirubin but also the photoproducts, and the reaction of patients' serum bilirubin was completed in 2 or 3 min. The change in the measurement values obtained using this diazonium salt before and after irradiation with a fluorescent lamp was smaller than that obtained by the enzymatic method or the diazo method using the diazotized sulfanilic acid.