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Phenylketonuria (PKU) is a disease in which the body lacks an enzyme that digests an amino acid called phenylalanine. Phenylalanine is most often found in foods that contain protein, such as meat, cow's milk, over-the-counter infant formula, and breast milk.
The PKU test is part of routine testing that babies have at the hospital after birth (newborn metabolic screening). The test is usually done within 1–2 days after birth, or after your baby has had enough milk to get an accurate test result. It is typically done for all newborns. However, it is especially important to have this test if the newborn has a family history of PKU because the disease is passed from parent to child.
This test measures how much of an enzyme called phenylalanine hydroxylase is in the blood.
This enzyme is made in the liver. It converts the amino acid phenylalanine into a different amino acid called tyrosine. These amino acids are necessary for growth. However, too much phenylalanine can cause brain damage and intellectual disability. Having too little of the enzyme phenylalanine hydroxylase means that your child has too much phenylalanine in his or her body.
A blood sample is required for this test. It is usually collected through a needle prick in the back of the foot (heel stick).
Your child's test results will be reported as either positive or negative for PKU. Positive means that there is too little phenylalanine hydroxylase in your child's blood, and negative means that there is a normal amount.
A negative test result means that your child does not have PKU. This is considered a normal result.
A positive test result means that your child may have PKU and will need more testing. He or she may need to eat a special diet that excludes phenylalanine.
Talk with your child's health care provider about what your child's results mean.
This information is not intended to replace advice given to you by your health care provider. Make sure you discuss any questions you have with your health care provider.
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