Alpha-fetoprotein (AFP) is a protein produced primarily during fetal development by the fetal liver and yolk sac. While its levels are high in a developing fetus, AFP is found in very low, almost undetectable, amounts in the blood of healthy adult men and non-pregnant women.
Alpha Protein’s Role in Fetal Growth
During gestation, alpha-fetoprotein serves several functions for the developing fetus. It is considered the fetal equivalent of albumin, a major protein in adult blood plasma. AFP helps regulate fluid balance and transports various substances, including fatty acids, bilirubin, copper, and nickel, to fetal cells.
This protein also plays a part in immune regulation during pregnancy, potentially protecting the fetus from the mother’s immune system. Its presence is a normal part of healthy fetal development. AFP levels in fetal blood are naturally high and then decrease significantly after birth, reaching adult levels by around 8 to 12 months of age.
When Alpha Protein Levels Are Measured
Alpha-fetoprotein levels are measured for different reasons, depending on whether a person is pregnant. In pregnant individuals, AFP testing is a routine screening offered between the 14th and 22nd weeks of pregnancy. This maternal serum AFP (MSAFP) test is commonly part of a “triple screen” or “quad screen” panel, which assesses the risk of certain birth defects and genetic conditions.
Beyond pregnancy, AFP is also used as a tumor marker for specific cancers. Elevated AFP levels in non-pregnant adults can indicate conditions such as liver cancer (hepatocellular carcinoma), testicular germ cell tumors, and certain ovarian cancers. It can also be elevated in other conditions like cirrhosis and hepatitis, indicating liver damage and regeneration.
What Alpha Protein Results Indicate
Interpreting alpha-fetoprotein results depends heavily on the individual’s circumstances. In pregnancy, unusually high AFP levels can suggest potential neural tube defects, such as spina bifida or anencephaly. Elevated levels may also point to abdominal wall defects, an inaccurate calculation of the due date, or a multiple pregnancy.
Conversely, low AFP levels during pregnancy may indicate an increased risk of chromosomal abnormalities, including Down syndrome (Trisomy 21) or Edwards syndrome (Trisomy 18). These are screening indications and not definitive diagnoses; many factors can influence AFP levels, and an abnormal result does not automatically mean a problem exists.
In non-pregnant individuals, elevated AFP levels can strongly suggest the presence of liver cancer, especially in individuals with chronic liver disease like cirrhosis. High AFP levels can also be seen with germ cell tumors of the testicles or ovaries.
Following Up on Abnormal Alpha Protein Levels
When alpha-fetoprotein test results are outside the typical range, further investigation is always recommended to determine the underlying cause. For pregnant individuals with abnormal AFP screening results, additional tests are usually performed. These often include a more detailed ultrasound to confirm gestational age, check for multiple pregnancies, and examine fetal anatomy for any structural anomalies.
If concerns persist, diagnostic procedures like amniocentesis may be offered. This involves taking a sample of the amniotic fluid to directly measure AFP levels and perform chromosomal analysis. Genetic counseling is also typically provided to help individuals understand the results and their implications.
For non-pregnant individuals with elevated AFP, further evaluation generally involves imaging studies such as ultrasound, CT scans, or MRI of the liver and other relevant areas. Blood tests for other tumor markers or liver function tests may also be ordered. In some cases, a biopsy of suspicious tissue may be necessary to confirm a diagnosis.