Measurement of bilirubin in serum is by

Measurement of Bilirubin in SerumQuantitation of bilirubin employs a colorimetric method based on the reddish-purple color formed when bilirubin reacts with diazotized sulfanilic acid. An assay conducted in the absence of added methanol measures "direct bilirubin," which is bilirubin glucuronide. An assay conducted in the presence of added methanol measures total bilirubin. The difference between total bilirubin and direct bilirubin is known as "indirect bilirubin," and is unconjugated bilirubin.Ref: Harper&;s Biochemistry; 30th edition; Chapter 31; Porphyrins & Bile Pigments