Alpha-fetoprotein (AFP) is a protein that serves a specific biological purpose during development in the womb. It is the most abundant protein in the bloodstream of a developing fetus, but its levels drop dramatically shortly after birth. In adult medicine, AFP is primarily used as a tumor marker, a substance measured in the blood that can be elevated in the presence of certain cancers or other conditions. Understanding the context of an AFP result requires knowledge of typical values and the limitations of this blood test.
Alpha-fetoprotein: Function and Measurement
Alpha-fetoprotein is a glycoprotein produced mainly by the fetal liver and the yolk sac during development. Structurally, it is considered the fetal equivalent of albumin, the most common protein in adult blood plasma. AFP acts as a carrier molecule, transporting substances like fatty acids and hormones through the fetal bloodstream.
After the first year of life, AFP production almost completely ceases, and only trace amounts remain detectable in the blood of healthy individuals. This low adult level allows the protein to be utilized as a marker for certain diseases. The AFP test measures the concentration of this protein in the blood serum.
The measurement of AFP is reported in nanograms per milliliter (ng/mL), reflecting the very small quantities typically present in the adult body. A simple blood draw is the standard procedure for this test. While AFP is not a perfect screening tool for cancer in the general population, its measurement is valuable for monitoring specific conditions and assessing treatment effectiveness.
Defining Standard AFP Range Values
A result of 2.0 ng/mL falls comfortably within the typical reference range considered normal for non-pregnant adults. The standard upper limit for AFP is usually cited as less than 10 ng/mL, though many laboratories set thresholds lower, often at 5 ng/mL or 7 ng/mL. The average AFP concentration in a healthy adult is generally in the range of 2 to 4 ng/mL, making 2.0 ng/mL an expected finding.
The exact reference interval can vary between different clinical laboratories due to variations in testing equipment and assays. Healthcare providers always consult the specific reference range provided by the performing lab. However, 2.0 ng/mL is universally interpreted as a non-elevated result in the adult context.
The low adult range contrasts sharply with levels found in newborns and pregnant individuals. AFP levels are naturally high at birth, sometimes reaching tens of thousands of ng/mL, before declining rapidly over the first year. In pregnant individuals, AFP levels rise significantly throughout the second and third trimesters as the protein transfers from the fetus into the maternal circulation.
Clinical Significance of Elevated AFP
An elevated AFP result suggests rapid cell division or tissue damage, which can be linked to cancer or non-cancerous liver conditions. The most common malignancy associated with AFP elevation is Hepatocellular Carcinoma (HCC), the primary form of liver cancer. In patients with chronic liver disease, a sudden rise in AFP, often above 200 ng/mL or 400 ng/mL, suggests HCC.
AFP is also a marker for certain types of Germ Cell Tumors (GCTs), which occur most often in the testicles or ovaries. Non-seminomatous GCTs (e.g., yolk sac tumors and embryonal carcinomas) frequently produce and secrete AFP. In these cases, the AFP level can be extremely high, sometimes reaching thousands of ng/mL.
An elevated AFP result does not automatically signify cancer, as several non-cancerous conditions can also cause an increase. Conditions involving chronic liver injury, such as cirrhosis or chronic hepatitis (B or C), frequently lead to moderately raised AFP levels, typically below cancer thresholds. The protein can also rise temporarily during liver regeneration following trauma or injury.
For patients already diagnosed with an AFP-producing tumor, the marker is used primarily for monitoring treatment effectiveness, not for initial diagnosis. Sequential measurements track the tumor burden. A rapid drop in AFP after therapy often indicates a positive response, while a subsequent rise may signal tumor recurrence.
Interpreting Results and Follow-Up
The AFP test is best understood as a screening or monitoring tool and should not be used as the sole basis for a medical diagnosis. The test’s utility is limited because many people with HCC or GCTs do not have elevated AFP, and non-cancerous liver conditions can cause abnormal results. Interpretation must always be done in conjunction with a person’s complete medical history, physical exam findings, and imaging results.
For individuals undergoing treatment, the rate at which the AFP level declines is a significant indicator of treatment success. Since AFP has a known biological half-life of approximately five to seven days, a measurement taken too soon after treatment may not accurately reflect the response. Clinicians use this half-life to calculate the expected drop, and a failure to drop as expected can indicate persistent disease.
If an AFP level is significantly elevated, further specialized testing is warranted. This includes imaging studies (ultrasound, CT scan, or MRI) to look for tumors in the liver or reproductive organs. An additional test, the AFP-L3%, compares a specific form of AFP (L3) to the total AFP, offering a more specific indicator of HCC risk, especially for patients with underlying cirrhosis. Discussing results with a healthcare provider who can evaluate the full clinical picture remains the most important step.