What tests are available for measuring AFP?
Several assays (tests) for measuring AFP in the blood are available. Generally, normal levels of AFP are below 10 ng/ml. Patients with various types of acute and chronic liver diseases without documentable liver cancer can have mild or even moderate elevations of AFP, though usually less than 500 ng/ml.
An AFP test is usually not done at home or a doctor's office; it is usually done in a hospital lab or a reference lab.
The use of the AFP assay in prenatal, perinatal, and pediatric care is beyond the scope of this discussion. We will confine the discussion to its use as a tumor screening test and as a tumor marker.
What is the sensitivity of AFP for diagnosing liver cancer?
Primary liver cancer, or hepatocellular carcinoma or hepatoma, is more common in some forms of chronic liver disease. As a screening test in patients with chronic hepatitis B and C, or hemochromatosis, AFP has a sensitivity for liver cancer of about 60%. In other words, an elevated AFP blood test is seen in about 60% of liver cancer patients. That leaves 40% of patients in these high-risk groups who can have liver cancer but have normal AFP levels. Consequently, the test is not diagnostic but is an indicator of a potential situation. Therefore, a normal AFP does not exclude liver cancer. For example; AFP levels are normal in a fibrolamellar carcinoma, a variant of hepatocellular carcinoma. Also, as noted above, an abnormal AFP does not mean that a patient has liver cancer. It is important to note, however, that patients with cirrhosis and an abnormal AFP, despite having no documentable liver cancer, still are at very high risk of developing liver cancer. Thus, any patient with cirrhosis and an elevated AFP, particularly with steadily rising blood levels, will either most likely develop liver cancer or actually already have an undiscovered liver cancer.
An AFP greater than 500 ng/ml is very suggestive of liver cancer. In fact, the blood level of AFP loosely relates to (correlates with) the size of the liver cancer.
Finally, in patients with liver cancer and abnormal AFP levels, the AFP may be used as a marker of response to treatment. For example, an elevated AFP is expected to fall to normal in a patient whose liver cancer is successfully removed surgically (resected). If AFP then increases again, liver cancer recurrence is likely.
In non-seminomatous germ cell cancers of the testis, the AFP is measured at diagnosis, and followed as a tumor marker in a fashion similar to that described above in resected hepatocellular carcinoma patients.
United States. National Cancer Institute. "Tumor Markers." Nov. 4, 2015. <http://www.cancer.gov/about-cancer/diagnosis-staging/diagnosis/tumor-markers-fact-sheet>.
University of Rochester Medical Center. "Alpha-Fetoprotein Tumor Marker (Blood)." <http://www.urmc.rochester.edu/encyclopedia/content.aspx?ContentTypeID=167&ContentID=alpha_fetoprotein_tumor_marker>.