Alpha-Fetoprotein Test Health Article

Precautions

It is very important that the doctor know precisely how old the fetus is when the test is performed, because the AFP level considered normal changes over the length of the pregnancy. Errors in determining the age of the fetus lead to errors when interpreting the test results. Since an AFP test is only a screening tool, more specific tests must follow to make an accurate diagnosis. An abnormal test result does not necessarily mean that the fetus has a birth defect. The test has a high rate of abnormal results (either high or low) in order to prevent missing a fetus that has a serious condition.

Preparation

There is no specific physical preparation for the AFP test.

Aftercare

Other than making sure the bleeding stops from the needle puncture site and watching for any signs of infection at the needle site, there is no specific aftercare involved with this blood test.

Risks

The risks associated with drawing blood are minimal but may include bleeding from the puncture site, feeling faint or lightheaded after the blood is drawn, or blood accumulating under the puncture site (hematoma).

Normal results

Alpha-fetoprotein is measured in nanograms per milliliter (ng/mL) and is expressed as a probability. The probability 1:100, for example, translates into the chance that the fetus has a one in 100 chance, for example, of having the defect. An AFP level less than or equal to 50 ng/mL is considered normal.

Abnormal results

The doctor inform the mother of the fetus about the specific increased risk as compared to the normal risk of a standard case. If the risk of Down syndrome is greater than the standard risk for women who are 35 years old or older (1:270), then amniocentesis is recommended. Again, the test has a high rate of showing an abnormal AFP level in order to prevent missing a fetus that has Down syndrome. This screening test only predicts risk; appropriate diagnostic testing follows an abnormal screening result. In neonatal liver disease testing, an AFP level greater than 40 ng/mL is considered abnormal. An AFP level greater than 20 ng/mL may be associated with tumors of the ovary or testes.

Parental concerns

A parent might be concerned about drawing blood from a child, but the pain from the needle puncture only lasts a moment.

When to call a doctor

If there is excess bleeding from the needle puncture site, or if hours to days later, the puncture site looks infected (red and swollen), then a doctor should be contacted.

BOOKS

Henry, John. Clinical Diagnosis and Management by Laboratory Methods, 20th ed. Philadelphia: Saunders, 2001.

Wallach, Jacques. Interpretation of Diagnostic Tests, 7th ed. Philadelphia: Lippincott, Williams, and Wilkins, 2000.

ORGANIZATIONS

March of Dimes Birth Defects Foundation. 1275 Mamaroneck Ave., White Plains, NY 10605. Web site: <www.modimes.org>.

National Cancer Institute. Building 31, Room 10A31, 31 Center Drive, MSC 2580, Bethesda, MD 20892–2580. Web site: <www.nci.nih.gov>.

Mark A. Best