What the AFP test shows
Alpha-fetoprotein (AFP) is a glycoprotein made in large amounts before birth — in the fetal yolk sac, liver and gut. It switches off in infancy, so healthy children and non-pregnant adults keep only a trace. The StatPearls reference calls it a fetal protein “re-expressed” in certain adult tumors — and that is what the test looks for.
AFP is read in two very different settings. In a non-pregnant adult it is a tumor marker, used mainly for primary liver cancer (hepatocellular carcinoma, HCC) and germ cell tumors of the testis and ovary, as MedlinePlus describes. In pregnancy it is a separate screening test on the mother’s blood.
CEA and CA 19-9 track the colon, pancreas and bile ducts — not the liver or germ cells — so in a liver-mass work-up they run with AFP to tell a primary liver cancer from a secondary deposit or bile-duct tumor.
AFP normal range
AFP is reported in ng/mL, numerically identical to the SI unit µg/L (1 ng/mL = 1 µg/L). Orientation values for the non-pregnant state:
| Group | Orientation, ng/mL (= µg/L) |
|---|---|
| Adults, non-pregnant | up to ~10 |
| Adult men vs women | men run marginally higher |
| Pregnancy | physiologically raised — read as multiples of the median, not this range |
| Newborns and infants | very high at birth, falling to the adult level by ~1–2 years |
Two numbers matter more than the “normal” upper limit. On surveillance the AASLD treats an AFP of 20 ng/mL or more, or a level climbing over consecutive tests, as a trigger for imaging; a value above roughly 400 ng/mL with a liver mass strongly suggests HCC. Because assays differ, reference ranges depend on the lab, sex and age — always read your result against your own report.
Why AFP is high
A raised AFP is more often a sign of a busy or damaged liver than of cancer. Roughly by frequency:
- Benign liver disease (commonest). Chronic hepatitis B and C, cirrhosis, fatty (metabolic) or alcohol-related liver disease and recovery from acute hepatitis all lift AFP as liver cells regenerate — usually mildly, moving with the liver enzymes ALT and AST.
- Pregnancy. AFP rises normally in pregnancy; a high maternal level on prenatal screening can flag a neural-tube (spina bifida, anencephaly) or abdominal-wall defect, per MedlinePlus.
- Hepatocellular carcinoma (HCC). The classic malignant cause: a high or rising AFP in cirrhosis or chronic hepatitis is a red flag, and higher values track larger tumors — though many small HCCs make none.
- Germ cell tumors. Non-seminomatous testicular and ovarian tumors (yolk-sac and embryonal types) can push AFP very high; they are worked up with beta-hCG and LDH.
- Other cancers (less common). Some stomach, pancreatic, bile-duct and lung cancers occasionally secrete AFP.
When is it urgent? A markedly high or rising AFP in liver disease, or any raised AFP with a liver mass or testicular lump, needs prompt specialist review. In a young man, a testicular mass with a high AFP is a germ cell tumor until proven otherwise.
Why AFP is low
For a tumor marker, a low AFP is the normal, reassuring result: there is no “AFP-deficiency” disease, and a trace level is what a healthy non-pregnant adult should have. Low matters in two situations.
The first is monitoring. After treatment of an AFP-producing cancer the level should fall — AFP’s half-life is about five to seven days — and MedlinePlus notes it usually normalizes within a month; a level that fails to fall, or later climbs, is often the earliest sign of remaining or returning tumor.
The second is pregnancy — the one setting where a low reading is itself a flag, raising the estimated risk of Down syndrome (trisomy 21) or trisomy 18. But a normal or low AFP never rules cancer out, because many liver and germ cell tumors are “AFP-negative” and are followed by imaging instead.
What to test alongside
AFP is rarely read alone. Around it sit the liver work-up and a few cross-checks:
- ALT and AST — liver enzymes; a mild AFP rise that moves with them usually means benign liver activity, not a tumor.
- CEA — a broad gut-cancer marker; helps tell a metastatic liver deposit from a primary HCC.
- CA 19-9 — the bile-duct and pancreatic marker; separates cholangiocarcinoma from HCC in a liver mass.
- Ferritin — very high levels point to iron overload (hemochromatosis), a cause of the cirrhosis behind liver cancer.
- HbA1c — flags the diabetes and metabolic syndrome behind fatty-liver disease, now a leading route to cirrhosis and HCC.
Also used in specialist care (no page here): beta-hCG and LDH for germ cell tumors; AFP-L3 and PIVKA-II (DCP), liver-specific refinements of AFP; and ultrasound, the partner in six-monthly surveillance.
What to do about an abnormal result
- Don’t panic over a mild rise, and don’t self-diagnose. A slightly high AFP is far more likely benign liver activity — hepatitis or fatty liver — than cancer, and one value is never the whole story.
- Repeat and trend. AFP is most useful as a trend, so an abnormal value is rechecked with liver enzymes, not acted on alone.
- Match the level to the next step. In someone at risk, a rising AFP or a level of 20 ng/mL or more prompts imaging (ultrasound, then CT or MRI); a testicular lump prompts a scrotal ultrasound with beta-hCG and LDH.
- See the right doctor. Start with your primary-care physician, who arranges imaging and refers on — to a hepatologist for the liver, or a urologist or oncologist for a germ cell tumor.
- Use it as guidelines intend. The AASLD pairs AFP with six-monthly ultrasound in people with cirrhosis or chronic hepatitis B; it is not a stand-alone test for the general population.
Mini-FAQ
What does a high AFP mean?
Most mild rises come from benign liver conditions — hepatitis, cirrhosis, fatty-liver disease — where the liver is regenerating. A high or rising level with liver disease raises concern for liver cancer; in a young man with a testicular lump it points to a germ cell tumor.
Can AFP be normal if I have cancer?
Yes. Around a third of liver cancers, and many germ cell tumors, never raise AFP, so a normal result does not rule cancer out — imaging is not skipped just because AFP is normal.
Is AFP a good screening test for liver cancer?
Not on its own. Guidelines pair it with a six-monthly abdominal ultrasound in high-risk people, such as those with cirrhosis or chronic hepatitis B; used alone it misses too many cancers and raises too many false alarms.
Why is AFP measured in pregnancy?
In pregnancy AFP is a different test on the mother’s blood: a high level can signal a neural-tube or abdominal-wall defect, a low level Down syndrome or trisomy 18. It is read as a multiple of the median, not the adult range.
What AFP level is worrying?
In an adult at risk of liver cancer, above about 400 ng/mL with a liver mass strongly suggests hepatocellular carcinoma, while 20 to 400 is indeterminate and needs imaging and a repeat test. Thresholds are lab-specific, and the trend matters more than one number.
How quickly should AFP fall after treatment?
AFP’s half-life is about five to seven days, so after an AFP-producing tumor is removed the level should fall toward normal within about a month. A plateau or later climb suggests tumor tissue remains or has returned.
