A comment on the fractional indirect diazo reaction.

Laurence and Abbott (1956) published a description of a micro-method for the estimation of serum bilirubin by the indirect diazo reaction. They indicated that two patterns of colour development are obtainable with foetal and adult sera from cases of severe haemolytic disease due to Rh incompatibility and from obstructive jaundice due to blockage of the common bile duct from carcinoma of the head of the pancreas (personal communication). Adult sera were described as exhibiting a rapid change in colour with maximum colour development at approximately 10 minutes of starting the reaction. Foetal sera exhibited a slower change, maximum colour developing at approximately 30 minutes from starting the reaction. Commercial "pure" bilirubin was found to give a pattern similar to that of foetal sera. These differences in behaviour were interpreted by the authors as indicating the existence of different " adult " and " foetal " substances which gave the indirect diazo reaction in sera. The implications of such a finding are farreaching with regard to both theoretical and clinical considerations. This study was undertaken to investigate whether different patterns of colour development were obtainable with the indirect diazo reaction using both normal and pathological, adult and foetal sera.