Difficulty: Medium
Average Score: 80%
Full-length
Newborns are routinely screened for phenylketonuria. The nursery nurse ensures that this screening test is performed:
Correct answer
B
Rationale
The infant has not ingested any protein immediately after birth, which is necessary to detect excessive serum phenylalanine. It is important that the infant take in 2-3 full days of milk or formula feedings to preclude a false-negative reading. At 2-3 days of age, inadequate milk could have been ingested owing to a delay in the initial feeding. The biochemical buildup of serum phenylalanine is detectable after 2-3 days of milk or formula ingestion.