Alpha-fetoprotein (AFP) testing is a common screening tool in healthcare. This blood test is primarily used during pregnancy to assess fetal well-being, but it also plays a role in detecting certain medical conditions in adults.
The Role of Alpha-Fetoprotein
Alpha-fetoprotein is a protein produced in significant amounts during fetal development. It is synthesized mainly by the fetal yolk sac and then by the fetal liver. This protein is present in the fluid surrounding the fetus, known as amniotic fluid, and can cross into the mother’s bloodstream. In the developing fetus, AFP functions similarly to albumin, acting as a carrier protein. After birth, AFP levels in the body decrease rapidly, and only very small amounts are typically found in healthy children and adults.
Conditions Detected by AFP Testing
AFP testing is utilized to screen for specific conditions, both during pregnancy and in non-pregnant individuals. During pregnancy, it is often included as part of a “multiple marker screen” to assess the risk of certain fetal abnormalities.
Elevated AFP levels in maternal blood can indicate a higher risk for neural tube defects, such as anencephaly (absence of brain/skull) or spina bifida (incomplete spinal column closure). These defects allow AFP to leak from the fetal circulation into the amniotic fluid and subsequently into the mother’s blood. High AFP levels can also suggest abdominal wall defects, including omphalocele (organs protrude into a sac) and gastroschisis (organs exposed without a protective membrane).
Conversely, lower-than-expected AFP levels in maternal blood can be associated with an increased risk of chromosomal abnormalities, such as Down syndrome (Trisomy 21) and Edwards syndrome (Trisomy 18).
In non-pregnant adults, AFP serves as a tumor marker. It is a key marker used for screening and monitoring individuals at higher risk for liver cancer, specifically hepatocellular carcinoma, especially those with chronic liver diseases like cirrhosis or hepatitis. Elevated AFP can also be a marker for certain germ cell tumors, which include specific types of testicular and ovarian cancers.
Understanding Your AFP Test Results
Interpreting AFP test results involves understanding what elevated, low, or normal levels might signify. If AFP levels are higher than expected during pregnancy, it could indicate a neural tube defect, an abdominal wall defect, or even a multiple pregnancy, such as twins. Sometimes, an elevated result simply means the estimated gestational age of the pregnancy was incorrect.
In adults, elevated AFP levels primarily suggest the presence of liver cancer or germ cell tumors.
Lower-than-expected AFP levels during pregnancy may point to an increased risk of chromosomal conditions like Down syndrome or Edwards syndrome. Similar to high levels, an inaccurate gestational age can also influence a low AFP result.
The AFP test is a screening tool, not a diagnostic one. An abnormal result does not definitively diagnose a condition; instead, it indicates a higher likelihood that a condition might be present and suggests the need for further investigation.
Next Steps After AFP Testing
If AFP test results are abnormal or concerning, healthcare providers typically recommend further evaluations. A detailed ultrasound is often the first step, as it can confirm the gestational age, identify multiple fetuses, and visually check for anatomical abnormalities like neural tube or abdominal wall defects.
If concerns persist, a more definitive diagnostic procedure like amniocentesis may be offered. This procedure involves taking a small sample of the amniotic fluid for analysis, which can definitively diagnose chromosomal abnormalities or neural tube defects.
Genetic counseling is also a crucial step, providing an opportunity to discuss the test results, understand potential implications, and explore all available options.
AFP testing has limitations, including the possibility of false positives, where a test indicates a problem that isn’t present, and false negatives, where a problem exists but the test is normal. Factors such as maternal weight or ethnicity can also influence test results.