Health Illustrated Encyclopedia
Alpha fetoprotein
Definition
Alpha fetoprotein (AFP) is a protein normally produced by the liver and yolk sac of a fetus. 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.
Alternative Names
Fetal alpha globulin; AFPHow the Test is Performed
Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.
Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.
Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.
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 fetus during pregnancy
- Diagnose certain liver disorders
- Screen for and monitor some cancers
During pregnancy, this AFP test can be done along with the examination of amniotic fluid (amniocentesis) to help detect fetal spina bifida or other birth defects.
Normal Results
The normal values in males or nonpregnant females is generally less than 40 micrograms/liter.
Note: Normal value ranges may vary slightly among different laboratories. 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 may be due to:
- Birth defects, including:
- Anencephaly
- Duodenal atresia
- Gastroschisis
- Omphalocele
- Spina bifida
- Tetralogy of Fallot
- Turner 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 light-headed
- 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.
Cunnigham FG, Leveno KL, Bloom SL, et al . Prenatal diagnosis and fetal therapy. In: Cunnigham FG, Leveno KL, Bloom SL, et al, eds. Williams Obstetrics. 22nd ed. New York, NY; McGraw-Hill; 2005:chap 13.
Provided by
Reviewed By: Linda Vorvick, MD, Seattle Site Coordinator, Lecturer, Pathophysiology, 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.
