Serum phenylalanine screening

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Circulatory system

Serum phenylalanine screening is a test for the disease phenylketonuria (PKU). The test detects abnormally high levels of phenylalanine.

Phenylalanine; Phenylalanine - serum

The test is usually included in routine screening tests, which are done before the newborn leaves the hospital. If the child is not born in the hospital, the test should be done in the first 1 - 2 weeks of life.

An area of the infant's skin, usually the heel, is cleaned with a germ killer (antiseptic) and punctured with a sharp needle or a lancet. Three drops of blood are placed in three separate test circles on a piece of paper. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

The test paper is taken to the laboratory where it is mixed with a type of bacteria that needs phenylalanine to grow, and another substance that blocks phenylalanine from reacting with anything else.

See also: Newborn screening tests

For help preparing your baby for the test, see infant test or procedure preparation (birth to 1 year).

When the needle is inserted to draw blood, some infants feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

This test is performed on infants to screen for phenylketonuria (PKU). This disease is caused by a deficiency of the enzyme needed to breakdown the amino acid phenylalanine.

If PKU is not detected early, an affected infant will become mentally retarded as the amino acid level builds up. However, if it is detected early, the severe side effects of PKU may be avoided through diet modification. Therefore, even though the condition is relatively rare, most newborns are screened.

Review Date: 10/23/2006
Reviewed By: John Goldenring, MD, MPH, JD, Department of Pediatrics, Children's Hospital, San Diego, CA. Review provided by VeriMed Healthcare Network.