Alpha-fetoprotein (AFP) is a protein normally produced in large amounts by a developing fetus. In healthy, non-pregnant adults, AFP levels in the blood are very low. When levels rise, it can signal the presence of certain cancers, most commonly liver cancer or specific types of testicular cancer. That’s what makes it useful as a tumor marker: a measurable substance in the blood that can help detect, diagnose, and monitor cancer.
How AFP Works as a Tumor Marker
Tumor markers are substances produced by cancer cells (or by the body in response to cancer) that show up in blood tests. AFP is the most widely used tumor marker for detecting liver cancer, specifically a type called hepatocellular carcinoma. Certain cancers essentially restart the production of this fetal protein, releasing it into the bloodstream at detectable levels. A simple blood draw is all it takes to measure it.
AFP isn’t a perfect screening tool on its own. Studies show its sensitivity for catching early-stage liver cancer ranges from 39% to 64%, meaning it misses a significant number of cases. Its specificity, the ability to correctly rule out cancer when it’s not present, is better at 76% to 97%. Because of these limitations, AFP is typically used alongside liver ultrasound rather than as a standalone test.
Which Cancers Cause Elevated AFP
The two main cancer types associated with high AFP are liver cancer and certain testicular cancers. In liver cancer, the tumor cells themselves produce AFP, and rising levels often reflect a growing tumor burden. This makes AFP valuable not just for initial detection but for tracking how well treatment is working.
In testicular cancer, AFP helps distinguish between different tumor types. It can be produced by nonseminomatous germ cell tumors, particularly those containing embryonal carcinoma, yolk sac tumor, or teratoma components. Seminomas, by definition, do not produce AFP. So if a patient with a testicular mass has elevated AFP, doctors know there is a nonseminomatous component present, which directly affects treatment planning. AFP is one of several tumor markers used together to diagnose, stage, and monitor testicular cancer.
Non-Cancer Causes of Elevated AFP
An elevated AFP result does not automatically mean cancer. Several non-cancerous conditions can push levels up, which is one reason the test has limited specificity. Chronic hepatitis and cirrhosis are the most common culprits. Both involve ongoing liver damage and inflammation, which can trigger AFP production even without a tumor present. Other forms of liver injury can do the same.
This overlap creates a clinical challenge. The very people most at risk for liver cancer (those with cirrhosis or chronic hepatitis) are also the ones most likely to have elevated AFP for non-cancerous reasons. That’s why imaging with ultrasound is so important as a companion test.
AFP in Liver Cancer Screening
For people at high risk of liver cancer, particularly those with cirrhosis or chronic hepatitis B or C, regular screening can catch tumors early when they’re more treatable. The American Association for the Study of Liver Diseases recommends surveillance using liver ultrasound, with or without AFP, every six months. Research suggests the combination of ultrasound plus AFP improves outcomes compared to either test alone, though the exact added benefit of AFP is still difficult to quantify from existing studies.
The recommendation to include AFP alongside ultrasound is classified as conditional, reflecting the imperfect evidence. Still, for high-risk patients, the combination remains the standard approach in clinical practice. The six-month interval is chosen because liver tumors typically grow slowly enough that this window catches most cancers before they advance to a stage where treatment options narrow.
Tracking Treatment and Detecting Recurrence
One of AFP’s most practical roles comes after a cancer diagnosis. Because AFP levels reflect tumor burden, doctors use it to gauge how well surgery, chemotherapy, or other treatments are working. After surgical removal of a liver tumor, a drop in AFP is considered a sign of successful treatment. Researchers have found that the ratio of AFP before surgery to the lowest AFP value within four months after surgery can help predict whether the cancer is likely to come back.
If AFP levels fall after treatment and then start rising again during follow-up blood work, that increase can be an early warning of recurrence, sometimes before a new tumor is visible on imaging. This makes regular AFP monitoring a straightforward way to keep watch in the months and years after cancer treatment. In testicular cancer, the same principle applies: AFP levels are tracked after treatment, and a rising trend can signal that residual or recurrent disease needs attention.
AFP During Pregnancy
AFP also plays an entirely separate role in prenatal screening. A developing fetus naturally produces large amounts of AFP, some of which crosses into the mother’s bloodstream. Measuring maternal AFP levels between 15 and 20 weeks of pregnancy can flag potential developmental concerns. Higher-than-expected levels may indicate a risk of neural tube defects like spina bifida or anencephaly, or certain abdominal wall defects. Lower-than-expected levels may suggest an increased risk of genetic conditions like Down syndrome or Edwards syndrome.
This prenatal use is a completely different application from the tumor marker test, even though the same protein is being measured. The context, timing, and interpretation differ entirely. If your doctor ordered an AFP test as part of cancer care or liver disease monitoring, the pregnancy screening information doesn’t apply to you.
What Your AFP Results Mean
AFP results are reported in nanograms per milliliter (ng/mL). In healthy, non-pregnant adults, levels are normally very low. The interpretation of a result depends heavily on your medical history. A mildly elevated AFP in someone with known cirrhosis might simply reflect liver inflammation, while the same number in a patient with a suspicious liver mass on imaging carries more weight.
A single AFP value is often less informative than the trend over time. A level that’s rising on repeated tests is more concerning than a stable, mildly elevated number. This is why doctors typically order AFP at regular intervals rather than relying on a one-time result. The pattern of change, whether levels are climbing, stable, or falling, tells a clearer story than any single number.