Phenylketonuria (PKU) Screening
Reviewed
Also called: PKU newborn screening, PKU test
A PKU screening test measures the amount of a protein called phenylalanine (Phe) in a sample of a newborn's blood.
Specimen: Blood (heel stick)
Why this test may be ordered
- Routine newborn screening required for all newborns in the United States, usually performed 24-72 hours after birth.
- Older infants or children who were not screened at birth or have symptoms of PKU (e.g., seizures, developmental delays, musty odor) may be tested.
Preparation and collection
There are no special preparations needed for a PKU test. If your baby wasn't born in the hospital or if you left the hospital early, be sure to talk with your child's provider to schedule a PKU test as soon as possible.
A health care provider will clean your baby's heel with alcohol. Then the provider will stick the baby's heel with a small needle to collect a few drops of blood.
There is very little risk to your baby from a needle stick blood test. Your baby may feel a little pinch when the heel is poked. A small bruise may form on the heel, but it should go away quickly.
Understanding results
To get accurate test results, the baby needs to have some protein from breast milk or formula before the blood sample is taken.
- Normal: If the results are normal, it means that the amount of Phe in your baby's blood was normal. So, your baby is unlikely to have PKU. Limitation: But if the test was done sooner than 24 hours after birth, your baby may need to be tested again at 1 to 2 weeks of age. Next step: If both parents know they carry a gene for PKU and your baby's test is normal, the baby should have genetic testing.
- Not normal (high Phe): If your baby's results are not normal, it means high levels of Phe were found in your baby's blood. Your baby most likely has PKU. Limitation: PKU can vary from mild to severe, depending on whether the changed gene still works somewhat or has stopped working completely. Next step: Your provider may order more tests to confirm or rule out PKU. These tests may include more blood tests and/or urine tests.
- The test is a screening, not a definitive diagnosis. Further testing is needed to confirm or rule out PKU.
- If performed before 24 hours after birth, a repeat test at 1-2 weeks of age may be necessary.
What to do next
If your baby is diagnosed with PKU, you can safely give your baby formula that doesn't contain Phe. Breastmilk does contain Phe, so if you would like to breastfeed, talk with your baby's provider to find out if your baby can safely have any amount of breastmilk.
- What does my baby's test result mean?
- Is further testing needed?
- What are the next steps for my baby's health?
- How can I ensure my baby's safety if the result is screen-positive?
Evidence source
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.
U.S. National Library of Medicine: Phenylketonuria (PKU) Screening