Tests and diagnosis

By Mayo Clinic Staff

Newborn blood testing identifies almost all cases of phenylketonuria. All 50 states in the United States require newborns to be screened for PKU. Many other countries also routinely screen infants for PKU.

If you have PKU or a family history of it, your doctor may recommend screening tests before pregnancy or birth. It's possible to identify PKU carriers through a blood test.

Testing your baby after birth

A PKU test is done a day or two after your baby's birth. The test isn't done before the baby is 24 hours old or before the baby has ingested some protein in the diet to ensure accurate results.

  • A nurse or lab technician collects a few drops of blood from your baby's heel or the bend in your baby's arm.
  • A laboratory tests the blood sample for certain metabolic disorders, including PKU.
  • If you don't deliver your baby in a hospital or are discharged soon after the birth, you may need to schedule a newborn screening with your pediatrician or family doctor.

If this test indicates your baby may have PKU:

  • Your baby may have additional tests to confirm the diagnosis, including more blood tests and urine tests
  • You and your baby may undergo genetic testing to identify gene mutations
Nov. 26, 2014

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