Serum phenylalanine screening

Serum Phenylalanine Screening

Serum phenylalanine screening, also known as fetal phenylalanine test, is a test done to detect abnormally high levels of phenylalanine in pregnant women. It is usually given to determine if a woman is at risk of having a baby with phenylketonuria (PKU), an inherited disorder where the body is unable to break down the naturally occurring amino acid, phenylalanine, which leads to severe mental and physical handicaps.

Preparation for the test

Typically, the test is usually ordered by a doctor or midwife associated with the prenatal care. It is generally recommended to begin the test at 16 weeks of pregnancy, and can be repeated between 24 to 28 weeks. Certain factors such as being a carrier for PKU, family medical history, or mother's age, may influence when the test should be administered. Depending on the availability of a specific laboratory test, an overnight or a two-step fasting test may be used.

Procedure

In order to accurately measure the levels of phenylalanine in the blood, a small sample of blood from the mother is collected in a special container and sent to a laboratory for analysis. The laboratory tests can detect very small amounts of phenylalanine in the sample, and the results are usually provided in two to three weeks.

Types

The test is usually done by either the Guthrie or the Guthrie-Drummond test, which both measure the level of phenylalanine in the blood. The Guthrie test requires a single blood sample, while the Guthrie-Drummond test requires two blood samples taken at different times.

Risks

While the test is generally considered to be safe and effective, there is the slight risk of infection when the sample is taken. Infection can be prevented with proper technique when the sample is taken.

Why and When Should it be Done?

• The test should be done when the mother or the father is known to be a carrier for the PKU gene.
• It is also beneficial to screen for phenylalanine if the mother is over the age of 35, as this age range has a higher risk for carrying the gene.
• It should also be done if there is a family medical history of PKU, or if the mother has had a previous pregnancy with a baby affected by PKU.

Conclusion

Serum phenylalanine screening is an important test done to determine if a mother is at risk of giving birth to a baby with PKU. The test is safe and effective, and it should be done when the mother or the father is known to be a carrier for the PKU gene, or if the mother is over the age of 35, or if there is a family medical history of PKU, or a previous pregnancy with a baby affected by PKU. Once the test is done and the results are received, the doctor or midwife can discuss any preventative measures that need to be taken before the baby is born.