Diazo reagent composed of diazo A and diazo B, as above described, combines with bilirubin to give a reddish purple compound known as azobilin. The intensity of this color can be measured in a colorimeter for a determination of the bilirubin present in the serum.
The most widely used method for bilirubin concentration determination is the diazo method, which measures the color of azobilirubin. The vanadate oxidase method is based on oxidation of bilirubin to biliverdin by vanadate.
Diazo compounds are used as precursors to carbenes, which are generated by thermolysis or photolysis, for example in the Wolff rearrangement. As such they are used in cyclopropanation for example in the reaction of ethyl diazoacetate with styrene.