Alpha-Fetoprotein (AFP, Maternal Serum Alpha-Fetoprotein [MSAFP], Triple Marker) Test
Test Description
Alpha-fetoprotein (AFP) is a globulin protein formed in the yolk sac and liver of the
fetus. As the fetus develops, the level of AFP found in the mother’s serum increases.
Only minute amounts of AFP remain in the bloodstream after birth.
This test is used primarily to screen for the presence of neural tube defects in
the fetus, such as spina bifida and anencephaly. The test, done between 15 and
20 weeks of pregnancy, does not absolutely diagnose a birth defect. However, if the
AFP is found to be abnormally high, additional testing, including ultrasonography
and testing of the amniotic fluid for AFP, is needed.
In many institutions, the test for AFP is now combined with measurement of
estriol and human chorionic gonadotropin. This combination testing is known by
various names, including “triple marker.” The measurement of these three substances
provides screening for neural tube defects, trisomy 18, and trisomy 21 (Down
syndrome). An accurate fetal gestational age is essential for accurate test results,
because the levels of the substances all vary with gestational age. The most
accurate method of assessing gestational age is ultrasonography; if unavailable,
gestational age by last menstrual period is used. This testing is a screening tool;
negative results do not guarantee a normal baby.
AFP is also considered a tumor marker for several types of cancer. Cancers typically
are characterized by undifferentiated cells. These cells often still carry surface
markers similar to those found in the fetus. The higher the AFP level, the
greater amount of tumor present. Thus, AFP can also be used to assess response to
cancer treatment.
THE EVIDENCE FOR PRACTICE
• Maternal serum AFP evaluation is an effective screening test for neural tube defects (NTDs)
and should be offered to all pregnant women.
• Women with elevated serum AFP levels should have a specialized ultrasound examination
to further assess the risk of NTDs.
Normal Values
Nonpregnant females/males: <40 ng/mL (<40 mg/L SI units)
Pregnant females: Reference laboratory provides normal values based
on gestational age.
Possible Meanings of Abnormal Values
Increased Decreased
Biliary cirrhosis Down syndrome
Breast cancer Fetal death
Colon cancer
Fetal distress
Fetal neural tube defect
Gastric cancer
Hepatic cancer
Hepatitis
Lung cancer
Multiple fetuses
Pancreatic cancer
Renal cancer
Testicular cancer
Contributing Factors to Abnormal Values
• Hemolysis of the blood sample may alter test results.
Interventions/Implications
Pretest
• Explain to the patient the purpose of the test and the need for a blood sample to be drawn.
• No fasting is required before the test.
Procedure
• A 7-mL blood sample is drawn in a red-top collection tube. (Note: Some laboratories use
a collection tube containing EDTA for the triple marker screening test.)
• Gloves are worn throughout the procedure.
Post test
• Apply pressure at venipuncture site. Apply dressing, periodically assessing for continued
bleeding.
• Label the specimen and transport it to the laboratory.
• Report abnormal findings to the primary care provider.
Clinical alert
• If the AFP is found to be abnormally high, additional testing, including ultrasonography
and testing of the amniotic fluid for AFP, is needed.
• For low-risk women considering becoming pregnant, folic acid supplementation
of 400 mcg per day is recommended because it has been shown to reduce the
occurrence and recurrence of neural tube defects.
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