A nurse is collecting a blood phenylketonuria (PKU) test for a newborn prior to discharge. The newborn's guardian asks the nurse what a positive PKU test would mean. Which of the following statements should the nurse make?

Choice A rationale A positive phenylketonuria (PKU) test indicates an inability to metabolize the amino acid phenylalanine, not galactose. Galactosemia is a separate metabolic disorder characterized by the body's inability to break down galactose, a sugar found in milk. Both are inborn errors of metabolism, but their biochemical pathways and dietary interventions differ significantly. Choice B rationale A positive PKU test does not indicate a slow metabolism in general. Instead, it specifically points to a deficiency in the enzyme phenylalanine hydroxylase (PAH), which is necessary for converting phenylalanine into tyrosine. This enzymatic defect leads to an accumulation of phenylalanine in the blood and tissues, which can become neurotoxic if untreated. Choice C rationale A positive finding for phenylketonuria (PKU) signifies a genetic disorder where the body lacks or has insufficient amounts of the enzyme phenylalanine hydroxylase. This enzyme is crucial for metabolizing the essential amino acid phenylalanine into tyrosine. Without proper enzyme function, phenylalanine accumulates in the blood, leading to neurotoxic effects if a specialized diet is not initiated promptly. Choice D rationale A positive PKU finding, if left untreated, directly leads to severe intellectual disability and other neurological problems due to the accumulation of phenylalanine, which is toxic to the developing brain. Therefore, it indicates an increased risk for neurologic anomalies if the condition is not managed through a strict low-phenylalanine diet from early infancy. .