Test guide
Phenylketonuria (PKU) Screening
A PKU screening test measures the amount of a protein called phenylalanine (Phe) in a sample of a newborn's blood. Phe is in all foods that contain protein such as milk, meats, and nuts. It's also in an artificial sweetener called aspartame. If a newborn has high levels of Phe in their blood, it could mean that they have phenylketonuria (PKU).
What it is for
A PKU test is used to see if a newborn has high blood levels of Phe in their blood. Though PKU is rare, all newborns in the United States are tested for it. That's because: If a newborn does have high Phe levels, that may mean that they have PKU. However, more tests may be needed to confirm or rule out a diagnosis. Source: MedlinePlus, National Library of Medicine. Medical test information is public domain. Source identity and definition checked automatically on 2026-10-18. No individual clinical interpretation or human reviewer is asserted.
Limitations
Reference intervals and interpretation depend on the laboratory, specimen, method and clinical context. This source definition is educational information; it does not establish a diagnosis, product approval or suitability for an individual.
Also known as
- PKU newborn screening, PKU test
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