Alpha-fetoprotein (AFP) is a plasma protein produced by the embryonic yolk sac and the fetal liver. AFP levels in serum, amniotic fluid, and urine functions as a screening test for congenital disabilities, chromosomal abnormalities, as well as some other adult occurring tumors and pathologies. This tumor marker is a glycoprotein encoded by the AFP gene on chromosome 4q25. Prenatal levels in developing human embryo rise from the end of the first trimester and begin to fall after 32 weeks of gestation. Maternal serum AFP forms part of the triple or quadruple screening tests for fetal anomaly.
A blood sample is collected from the vein using aseptic techniques and observing universal precautions. Serum alpha levels are measured either as part of a maternal triple or quadruple screening test or for other diagnostic purposes in non-pregnant female or male patients.
Urine samples collected in plain or universal bottles may also be assayed for alpha-fetoprotein levels, although this may be significantly lower in comparison to serum levels.
Amniocentesis is needed to be able to assay alpha-fetoprotein levels in the amniotic fluid. A diagnostic amniocentesis involves the use of an ultrasound-guided, hollow needle through the maternal anterior abdominal wall into the amniotic cavity to draw out amniotic fluid for AFP immunoassay.
Blood sample collection (phlebotomy):
Procedure for amniocentesis (done from 15 weeks gestation):
The following are reasons for AFP assay:
Pregnant maternal serum AFP levels elevated:
Pregnant maternal serum AFP low levels:
Non-pregnant female or male adult AFP elevated:
Typical findings include:
The following have been implicated in false positive results:
Risks associated with phlebotomy include:
The risk associated with amniocentesis:
Phlebotomy for the purpose of blood alpha fetoprotein assay requires little or no preparations, as this is largely safe when performed by qualified health workers. However, patients need to be counseled on the possible discomfort from needle prick, although mostly bearable. Patients must also be asked about their use of blood thinners (e.g., aspirin, warfarin).
Patients must also be given appropriate information regarding possible outcomes and implications of the test.
It is pertinent to explain that this is a screening test. Depending on the outcome, more tests may be ordered for the purpose of establishing a diagnosis. A negative test does not necessarily indicate no risk, as very low maternal blood alpha-fetoprotein is associated with increased incidence of Down syndrome. Hence, a low maternal blood alpha-fetoprotein should also be investigated.
Patients having amniocentesis must be duly counseled about the procedure, as well as, the associated risks. There is a risk of obstetric mishap following amniocentesis; a miscarriage can happen in less than 1% of cases. Some other very rare complications of amniocentesis are preterm labor, infection (amnionitis), iatrogenic trauma, or injury to developing fetus or mother.
Following amniocentesis patients may experience some cramp-like discomfort in the first few hours but are usually allowed to go home after a short rest. Oral paracetamol (acetaminophen) may be prescribed. Patients should report back to the hospital in case of vaginal bleeding, vaginal discharge, or increasing abdominal cramps.
Maternal blood AFP levels often as part of triple (AFP, Estriol, and hCG) or quadruple (AFP, implies Estriol, hCG and Inhibin A) screening test for birth defects. Levels are usually interpreted for age, race, weight, and gestational age. The elevated levels imply a significant risk of having birth defects, hence, further evaluation may be required to assess the level of risk.
A significant amount of patients with elevated maternal AFP do not develop birth defects, but there may be an increased risk of obstetric complications like premature rupture of membrane, placenta accreta, increta, and packet.
Low maternal AFP levels may be suggestive of risk for Down syndrome.
In nonpregnant women and men, elevated levels are seen in cancers, especially, liver cancer. Levels greater than 200 ng/ml in cirrhotic patients suggest hepatocellular carcinoma. Elevated alpha-fetoprotein levels can also be found in testicular and ovarian carcinoma.
AFP levels may also be used to evaluate response to anti-cancer therapy.