AFP (Alpha-Fetoprotein) Test

AFP, or Alpha-Fetoprotein, is a protein normally produced in large amounts by a developing fetus's liver and yolk sac, but present at only very low levels in the blood of healthy adults.

In adults, elevated AFP levels can be an important marker for certain cancers, most notably hepatocellular carcinoma (the most common type of primary liver cancer) and certain germ cell tumors of the testicles or ovaries.

The test serves two quite different clinical purposes depending on context: in adults, it helps screen high-risk patients (such as those with cirrhosis) for liver cancer and monitor known cancers, while during pregnancy, AFP is measured as part of a maternal screening panel for certain chromosomal or neural tube conditions in the developing baby — with completely different reference ranges applying in each context.

Because of these very different applications, it's important that AFP results always be interpreted with full knowledge of whether the patient is pregnant, has liver disease, or is being monitored for a known tumor.