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Newborn Screening ACT Sheet

[Increased Phenylalanine]
Phenylketonuria (PKU)


  • Contact family immediately to inform them of the newborn screening result.
  • Consult with pediatric metabolic specialist.
  • Evaluate the newborn and refer as appropriate.
  • Initiate confirmatory/diagnostic tests in consultation with metabolic specialist.
  • Provide the family with basic information about PKU and dietary management.
  • Report findings to newborn screening program.

Diagnostic Evaluation:

Plasma amino acid analysis which shows increased phenylalanine without increased tyrosine (increased phenylalanine:tyrosine ratio). Urine pterin analysis and red blood cell DHPR assay will identify pterin defects. Consider PAH mutation testing.

Clinical Considerations:

Asymptomatic in the neonate. If untreated PKU will cause irreversible mental retardation, hyperactivity, autistic-like features, and seizures. Treatment will usually prevent these symptoms. Pterin defects cause early severe neurologic disease (developmental delay/seizures) and require specific therapy.

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