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Tests and diagnosis
By Mayo Clinic staffNewborn screening identifies almost all cases of PKU. All 50 states in the United States require newborns to be tested for PKU. Many other countries also routinely screen infants for PKU.
If you have PKU or a family history of PKU, 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 conducted a day or two after your baby's birth. In the test, a nurse or lab technician collects a few drops of blood from your baby's heel or the crook of your baby's arm using a needle or lancet. A laboratory tests the blood sample for certain metabolic disorders, including PKU. 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. 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.
Your baby may also have additional tests to confirm the diagnosis, including more blood tests and urine tests. You and your baby may also undergo genetic testing to identify gene mutations.
If your baby's blood sample shows a high level of phenylalanine, he or she will need to be fed a special formula. Your doctor can help you find the right type of formula to feed your baby.
Screening during pregnancy
It's also possible to detect PKU in a developing fetus using chorionic villus sampling (CVS). During this procedure, a needle is inserted through a pregnant woman's lower abdomen and into the uterus. Another option is to insert a catheter up through the cervix into the chorionic villi, which forms the lining of the placenta. Through the needle, your doctor removes a small sample of cells for genetic testing. Your doctor and a genetics counselor can help you decide if these tests are right for you and what to do with the results.
- Bodamer OA. Overview of phenylketonuria. http://www.uptodate.com/home/index.html. Accessed Aug. 18, 2009.
- Phenylketonuria. Genetics Home Reference. http://ghr.nlm.nih.gov/condition=phenylketonuria. Accessed Aug. 27, 2009.
- PKU (Phenylketonuria). March of Dimes. http://www.marchofdimes.com/professionals/14332_1219.asp. Accessed Aug. 24, 2009.
- Longo Nicola. Inherited disorders of amino acid metabolism in adults. In: Fauci AS, et al. Harrison's Principles of Internal Medicine. 17th ed. New York, N.Y.: McGraw Hill Medical; 2008. http://www.accessmedicine.com/content.aspx?aID=2882866. Accessed Aug. 27, 2009.
- Amino acid and organic acid metabolism disorders. The Merck Manuals: The Merck Manual for Healthcare Professionals. http://www.merck.com/mmpe/print/sec19/ch296/ch296c.html. Accessed Aug. 27, 2009.
