AFP Test

Alpha-fetoprotein (AFP) is a protein naturally made by the fetus during pregnancy, mainly by the liver and yolk sac. In adults, AFP levels are normally very low. However, when they rise outside of pregnancy, it can suggest certain health problems, including cancers like hepatocellular carcinoma (HCC), which is the most common form of liver cancer, and some testicular and ovarian tumors.

Biologically, AFP acts somewhat like albumin, another protein that carries important substances like hormones, fats, and vitamins through the bloodstream. AFP is structured with complex sugar attachments and exists in several forms (called glycoforms), each telling a different story about the body’s condition. One specific form, AFP-L3, tends to be higher in people with liver cancer compared to those with liver inflammation alone.

In clinical practice, an AFP blood test is used in a few different ways:

• Cancer Detection: In patients with chronic liver diseases like hepatitis or cirrhosis, an AFP level over 20 nanograms per milliliter (ng/mL) might trigger further testing for liver cancer. However, the test is not highly sensitive or specific: about 60% of liver cancers are detected with this threshold, and many benign liver diseases can also raise AFP levels.
• Pregnancy Screening: In pregnancy, AFP is part of a group of blood tests to check for fetal development problems. High AFP may suggest issues like spina bifida (a birth defect of the spine), while low AFP can suggest chromosomal conditions like Down syndrome.
• Monitoring Treatment: Doctors use AFP levels to track cancer treatment response. After surgery or chemotherapy, falling AFP levels are a good sign. Rising levels may signal that the cancer has returned or spread.

AFP is not a perfect test. Many people with early-stage liver cancer have normal AFP levels, and many with elevated AFP do not have cancer. Non-cancerous conditions like hepatitis, cirrhosis, or even pregnancy naturally raise AFP. This is why AFP is rarely used alone; imaging tests (like ultrasound or MRI) and other blood markers are often combined for a more accurate picture.

Another specialized use of AFP is measuring the AFP-L3 percentage. This subset can be more specific for liver cancer and may help identify cancer earlier when standard AFP tests are inconclusive.

AFP is not a perfect test. Many people with early-stage liver cancer have normal AFP levels, and many with elevated AFP do not have cancer. Non-cancerous conditions like hepatitis, cirrhosis, or even pregnancy naturally raise AFP. This is why AFP is rarely used alone; imaging tests (like ultrasound or MRI) and other blood markers are often combined for a more accurate picture.

Another specialized use of AFP is measuring the AFP-L3 percentage. This subset can be more specific for liver cancer and may help identify cancer earlier when standard AFP tests are inconclusive.