This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: HAEM synth and porphyrias, Subject name: Biochemistry
Bilirubin binding capacity for high-affinity site of serum albumin is: 
Select and explain. 
A. 15 mg bilirubin/100 ml of plasma, B. 25 mg bilirubin/100 ml of plasma, C. 35 mg bilirubin/100 ml of plasma, D. 45 mg bilirubin/100 ml of plasma
B: 25 mg bilirubin/100 ml of plasma
Answer: B: 25 mg bilirubin/100 ml of plasma 
Explanation: 1 gram of hemoglobin yields about 35 mg of bilirubin. Human adults form 250 to 350 mg of bilirubin per day. Bilirubin is non-polar. So, it needs a carrier in blood. Albumin plays the role of carrier. The high-affinity site can bind approximately 25 mg of bilirubin/100 mL of plasma. Loosely bound bilirubin can be easily displaced by drugs like phenobarbitone. This is why administration of phenobarbitone in premature infants can lead to kernicterus.