This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of carbohydrate, Subject name: Biochemistry
Measurement of bilirubin in serum is by 
Select and explain. 
A. Colorimetric method, B. Electrophoresis, C. Spectrophotometry, D. Chromatography
A: Colorimetric method
Answer: A: Colorimetric method 
Explanation: 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