Alpha-fetoprotein (AFP) is a protein that is normally only produced in the fetus during its development. When found in adults, it can be used as a tumor marker. If high levels of AFP are found in amniotic fluid it can indicate a developmental defect in the baby. Genetic counseling is usually offered if an AFP screening test is positive.

Normal levels of alpha-fetoprotein in blood plasma are very low, though they will go up slightly during pregnancy. If levels are higher than this, it could possibly indicate that a pathological process is occurring.

Like all tumor markers, the detection of AFP by itself is not diagnostic of anything, although if it is detected it is certainly advisable to rule out the diseases could cause levels to rise. The primary reason tumour markers are used are to measure the success of a treatment (e.g. chemotherapy), if levels of AFP are going down, it is an indication that a disease is improving.

High AFP in non-pregnant adult

The two most devastating conditions in an adult that cause elevated AFP in an adult are testicular cancer and hepatocellular carcinoma (HCC) (a type of liver cancer). Hepatocellular carcinoma will often increase AFP levels dramatically.

As well as these, cirrhosis of the liver, and active hepatitis also elevate levels of alpha-fetoprotein.

High AFP in amniotic fluid

An amniocentesis can be done if an abnormality of a foetus is suspected.

Levels of AFP can be down slightly in Down's syndrome, and levels are frequently higher with neural tube defects such as spina bifida.

A multiple pregnancy, such as twins or triplets, also causes an increase in AFP levels.