Alpha-fetoprotein, or AFP, is a protein found normally in abundance in the developing fetus. Only very low levels of the protein are present in healthy children and adults, except for pregnant women. Elevated blood levels of AFP can be associated with liver disease, certain kinds of cancer and abnormal pregnancies.
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Alpha-fetoprotein is a major protein produced by the fetal yolk sac, a part of the early embryo that eventually disappears, and the fetal liver. Some of this protein leaks into the amniotic fluid and across the placenta, resulting in typically elevated AFP levels in pregnant women. Newborns have very high AFP levels, which drop rapidly over the first few months of life to the very low levels seen in children and adults, according to Lab Tests Online. Normal adult levels are less than 6 ng/mL, but can vary between different laboratories performing the test. Liver cells are the main source of AFP found in healthy non-pregnant people.
Benign Elevations of AFP
Mild to moderate elevations of AFP blood levels are seen with cirrhosis, viral hepatitis, other causes of chronic liver damage and normal pregnancy. Repair and regeneration of liver cells with liver disease results in release of additional AFP into the bloodstream, and AFP from the fetus leads to the higher levels seen in pregnant women. The rise in AFP in these conditions is typically less than 500 ng/mL and can fluctuate with the activity of the disease or the stage of pregnancy, according to the Family Practice Notebook. Small numbers of healthy people also have higher than expected AFP levels on an inherited basis and should not be confused with evidence of disease.
AFP in Pregnancy
A woman’s AFP level rises in a predictable manner throughout pregnancy as the fetus grows but can be altered by problems with the pregnancy. By comparing the woman’s measured AFP level to the average level of all women at the same gestational age, the result can be used as a screening test for possible problems in the developing fetus, according to Mayo Medical Laboratories. Abnormally high AFP levels indicate the possibility of a neural tube defect, or abnormality of the baby’s developing brain and spinal cord, as well as other developmental abnormalities, congenital kidney disease or increased risk of fetal loss. The test is not diagnostic, but indicates further evaluation should be performed. Higher AFP levels are also seen normally in multiple pregnancies, such as with twins or triplets, and accurate dating of gestational age is critical for comparison purposes in screening.
AFP as Tumor Marker
Certain tumors can produce elevated AFP blood levels, particularly hepatocellular carcinoma, or primary liver cancer, and some types of testicular and ovarian cancer. AFP is elevated in about 80 percent of hepatocellular carcinoma cases, often to levels well above 1,000 ng/ml. The high AFP levels associated with a tumor should return to normal following successful treatment, with rising levels after treatment indicating new tumor growth or recurrence.
People with cirrhosis and chronic hepatitis have an increased risk of developing liver cancer, and if their already moderately elevated AFP levels increase suddenly the change could indicate the emergence of cancer. Abnormal results should always be discussed with a health care practitioner.