Bilirubin binding capacity for high-affinity site of serum albumin is:: (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
Answer is B. 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.