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Alternative names Return to top
Phenylalanine; Phenylalanine - serumDefinition Return to top
Serum phenylalanine screening is a test for the disease phenylketonuria (PKU). The test detects abnormally high levels of phenylalanine.How the test is performed Return to top
An area of the infant's skin, usually the heel, is cleansed with 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 inhibits phenylalanine from reacting with anything else.
How to prepare for the test Return to top
For help preparing your baby for the test, see the following topic:How the test will feel Return to top
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.Why the test is performed Return to top
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.
Normal Values Return to top
A normal test results in no bacteria growth. This indicates that phenylalanine levels are normal.What abnormal results mean Return to top
Bacteria growth indicates that phenylalanine levels in the infant's blood are too high. PKU is a possibility and further testing will be performed.What the risks are Return to top
The risks of having blood drawn are slight, but include:
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Page last updated: 28 October 2004 |