The caregiver whose newborn was newly diagnosed with phenylketonuria (PKU) has questions about the disorder. Which statement made by the nurse is correct regarding PKU?

A. PKU is typically diagnosed through a blood test, not a urine test. The blood test measures phenylalanine levels, which are elevated in PKU. B. Untreated PKU can lead to severe cognitive deficits and developmental delays due to the accumulation of phenylalanine, which is toxic to the brain. Early detection and treatment can prevent these outcomes. C. In PKU, the urine does not typically contain high levels of phenyl pyruvic acid; it is the blood levels of phenylalanine that are elevated. D. The effects of PKU are not reversible; however, with early and consistent treatment, such as a strict low-phenylalanine diet, the symptoms can be managed effectively.