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Alpha fetoprotein
Definition
Alpha fetoprotein (AFP) is a protein normally produced by the liver and yolk sac of a developing baby during pregnancy. AFP levels decrease soon after birth. AFP probably has no normal function in adults.
A test can be done to measure the amount of AFP in your blood.
See also: Quadruple screen
Alternative Names
Fetal alpha globulin; AFP
How the Test is Performed
A blood sample is needed. For information on how this is done, see: Venipuncture
How to Prepare for the Test
There is no special preparation.
How the Test Will Feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the Test is Performed
Your doctor may order this test to:
- Screen for problems in the baby during pregnancy
- Diagnose certain liver disorders
- Screen for and monitor some cancers
During pregnancy, this AFP test can be done along with amniocentesis to help detect spina bifida or other birth defects in the developing baby.
Normal Results
The normal values in males or nonpregnant females is generally less than 40 micrograms/liter.
The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.
What Abnormal Results Mean
Greater than normal levels of AFP may be due to:
- Cancer in testes, ovaries, biliary (liver secretion) tract, stomach, or pancreas
- Cirrhosis of the liver
- Liver cancer
- Malignant teratoma
- Recovery from hepatitis
During pregnancy, abnormal levels of AFP (as part of a quadruple screen) may be due to:
- Birth defects, including:
- Genetic disorders, including Down syndrome
- Inaccurate due date
- Intrauterine death (usually results in a miscarriage)
- Multiple pregnancy (twins, triplets, etc.)
Risks
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
References
Simpson JL, Otaño L. Prenatal genetic diagnosis. In: Gabbe SG, Niebyl JR, Simpson JL, eds. Obstetrics: Normal and Problem Pregnancies. 5th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2007:chap 7.
Lee P, Pincus MR, McPherson RA. Diagnosis and management of cancer using serologic tumor markers. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. Philadelphia, Pa: Saunders Elsevier; 2006:chap 74.
Cunningham FG, Leveno KJ, Bloom SL, et al. Prenatal diagnosis and fetal therapy. In: Cunningham FG, Leveno KL, Bloom SL, et al, eds. Williams Obstetrics. 23rd ed. New York, NY: McGraw-Hill; 2010:chap 13.
Reviewed By: Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine; and Susan Storck, MD, FACOG, Chief, Eastside Department of Obstetrics and Gynecology, Group Health Cooperative of Puget Sound, Redmond, Washington; Clinical Teaching Faculty, Department of Obstetrics and Gynecology, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
