Definition
Serum phenylalanine screening is a test for the disease phenylketonuria (PKU). The test detects abnormally high levels of phenylalanine.
Alternative Names
Phenylalanine; Phenylalanine - serumHow the test is performed
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
How to prepare for the test
For help preparing your baby for the test, see infant test or procedure preparation (birth to 1 year).
How the test will feel
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
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
A normal test results in no bacteria growth. This indicates that phenylalanine levels are normal.
What abnormal results mean
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
The risks of having blood drawn are slight, but include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
- Multiple punctures to locate veins
| • | Phenylketonuria |
Reviewed By: John Goldenring, MD, MPH, JD, Department of Pediatrics, Children's Hospital, San Diego, CA. Review provided by VeriMed Healthcare Network.
