In the Jendrassik-Grof reaction for total bilirubin, bilirubin reacts with diazotized sulfanilic acid to form:

• A. Diazo bilirubin
• B. Biliverdin
• C. Azobilirubin
• D. Bilirubin glucuronide

Answer: (C)

In this colorimetric bilirubin assay, bilirubin reacts with a diazonium salt derived from sulfanilic acid. This coupling forms a colored azo compound called azobilirubin. The formation of azobilirubin provides the intense color that is measured to determine the bilirubin concentration, and this approach works for total bilirubin (including both unconjugated and conjugated forms). The other options don’t fit because they are not the product of this diazo-coupling reaction: biliverdin is a different pigment from heme breakdown, bilirubin glucuronide is the conjugated form found in bile, and the term diazo bilirubin isn’t the established description of the reaction product.