Phenylketonuria (PKU) Test

PKU (Phenylketonuria) Screening

What To Think About

• If your baby goes home within 24 hours of birth, the PKU test result may not be correct. Your baby may need to be tested again if the PKU results are not normal. When the test is done within 24 hours of birth, there is a small chance of having a PKU test be normal when your baby does have PKU. There is a very small chance of a false result if the test is done between 24 and 72 hours after birth.
• Sick babies or babies born early are usually tested for PKU soon after birth and then again at age 2 to 3 weeks.
• Testing may occur as often as once a week in your baby's first year and then once or twice a month throughout childhood.
• A blood test for phenylalanine may be done if you have PKU and plan to become pregnant. If you eat too much protein, you will have high levels of phenylalanine in your blood. If you become pregnant, the high levels of phenylalanine could cause mental retardation of your baby (fetus), even if your baby does not have PKU. It is important that everyone with PKU see a specialist for nutritional counseling. Phenylalanine levels should be below 6 mg/dL at least 3 months before you become pregnant. Recommended phenylalanine levels during pregnancy are 2 mg/dL to 6 mg/dL, and testing should occur at least once a week.
• A test for phenylalanine levels in urine may be done if your baby is now over 6 weeks of age and did not have a PKU blood test 2 to 3 days after birth. A PKU heel stick can be done up to 6 weeks of age and has better results than a urine test. A urine test may be done to check phenylalanine levels during treatment with low-protein foods.
• If your baby has PKU, a special low-protein diet is needed to prevent mental retardation. Your baby will drink milk substitutes that do not contain phenylalanine. People with PKU (especially women during their childbearing years) need to stay on a low-protein diet for life to prevent problems.

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Author:	Debby Golonka, MPH	Last Updated: February 27, 2008
Medical Review:	Michael J. Sexton, MD - Pediatrics Thomas Emmett Francoeur, MDCM, CSPQ, FRCPC - Pediatrics
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