What is the alpha-fetoprotein (AFP) blood test?
The most abundant plasma protein found in the human fetus is alpha-fetoprotein (AFP). AFP is a protein normally made by the immature liver cells in the fetus. At birth, infants have relatively high levels of AFP in the blood, which fall to normal low adult levels by the first year of life. Also, pregnant women carrying babies with neural tube defects may have high levels of AFP in both the bloodstream and in the amniotic fluid. A neural tube defect is an abnormal fetal brain or spinal cord that is caused by folic acid deficiency during pregnancy. Alpha-fetoprotein is also produced by certain cancers and is sometimes measured as a tumor marker. The AFP tumor marker test requires a blood sample. Other names for the test include total AFP and alpha-fetoprotein-L3 percent (%).
In which situations are high blood levels of AFP seen in adults?
In adults, high blood levels (over 500 nanograms/milliliter [or ng/ml]) of AFP are seen in only a few situations, such as
- hepatocellular carcinoma (HCC), a primary cancer of the liver;
- germ cell tumors (a type of cancer of the testes and ovaries);
- ataxia telangiectasia, a severely disabling and rare genetic neurodegenerative disease; and
- less commonly, in other types of cancer, including lymphoma or cancer of the lung, breast, or colon.