Azobilirubin is a coloured compound formed by the condensation of diazotized sulfanilic acid with bilirubin in the van den Bergh reaction.
[1] The quantity of bilirubin in patients with jaundice can be determined by the formation of azobilirubin in the presence of methanol.
[2] The Van den Bergh chemical reaction which is used to measure bilirubin levels, couples bilirubin with diazotized sulfanilic acid.
The presence of azobilirubin is best indicated by the emergence of a pink-purple color.
If we have high levels of bilirubin in the blood, the Van den Bergh chemical reaction is used to determine if the bilirubin is conjugated or unconjugated.