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 or babies born early are usually tested for PKU within 7 days after birth.
• The Canadian Task Force on Preventive Health Care recommends that infants tested in the first 24 hours of life be retested within 2 to 7 days of age.¹
• When a baby has PKU, the U.S. National Institutes of Health (NIH) recommends weekly PKU tests during the first year of life. From age 1 to 12 years, the NIH recommends tests twice a month. After age 12, tests may be done once a month.
• 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. If you have PKU, you should eat very low-protein foods before you become pregnant and continue that during your pregnancy. Phenylalanine levels should be below 6 mg/dL at least 3 months before you become pregnant. Recommended phenylalanine levels during pregnancy are 2 to 6 mg/dL. The National Institutes of Health (NIH) recommends blood tests twice a week throughout the pregnancy for women who have PKU.
• A test for phenylalanine levels in urine may be done if your baby is now over 6 weeks old 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 child-bearing years) need to stay on a low-protein diet for life to prevent problems.
• Most positive PKU tests turn out to be false-positives when more blood tests are done.

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Author:	Carrie Henley Jan Nissl, RN, BS	Last Updated: May 26, 2006
Medical Review:	Michael J. Sexton, MD - Pediatrics Thomas Emmett Francoeur, MDCM, CSPQ, FRCPC - Pediatrics
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