Alpha fetoprotein or alpha fetoglobulin is a major protein (70kD) secreted primarily by liver, Fetal yolk sac and gastrointestinal tract. It exists in three isoforms. L3 form is a widely accepted tumor marker in hepatocellular carcinomas. Genes on Chromosome 4 are responsible for production of AFP. After birth, the production of this protein declines rapidly. However, the isoforms are increased in specific cases such as cancer. Hence, the alpha fetoprotein measurements are of clinical use both during pregnancy and in adults.
What is alpha fetoprotein diagnostic?
Alpha fetoprotein diagnostic is a prenatal test used to test for anomalies in the fetus before birth. With this test, you can check for abnormalities in the development of fetus during pregnancy. The test is used to detect and measure the level of alpha fetoprotein which is an indicator of neural defects. The presence of abnormal levels of alpha fetoprotein in mother's blood indicates possible mental defects in the child. Alpha fetoprotein is produced in the womb by the fetus and passed on to mother's blood during pregnancy.
Who needs the test?
Pregnant mothers in second trimester (16-18 weeks) can undergo this test to find the measure of the alpha fetoprotein in their serum.
However, the neural tube defects form during early pregnancy even before one confirms pregnancy. This is because the formation of neural tube occurs within 28 days of conception. Finding out any abnormal neural tube defects would help the parents to prepare emotionally, socially and financially before birth. Neural tube defects occur almost once in every 1000 births and hence the need to find out these anomalies is also on the rise.
The protein is also a diagnostic tumor marker in liver cell cancer.
The test requires to draw very little blood of 50μL (approximately 2 drops of blood) to find the presence of the protein. Slightly higher volume is required to measure the concentration of AFP. Usually the test forms a part of the triple screening test or QUAD test which tests for other fetal proteins also during pregnancy.
Since the technique is non invasive, there is less risk to the fetus. Non invasive techniques are tests done on mother's blood which does not involve insertion of any probe or needle into the uterus.
The screening has high sensitivity for certain neural disorders and is one of the best non invasive methods to find neural tube defects during pregnancy.
The normal range of alpha fetoprotein in blood is less than 10ng/ml. An abnormally low level of alpha fetoprotein is an indicator of Down's syndrome which results in impairment of cognitive abilities which affect the normal functioning and coordination skills. It also causes impaired physical growth characterized by unusual facial and physical features.
A high level of alpha fetoprotein on the other hand indicates abnormalities in neural tube development, kidney problems, threatened miscarriage or even fetal death in womb.
However, these are indications only and should be confirmed by other tests and procedures. Low levels of AFP are found in every healthy pregnancy and therefore should not be considered as a sole judgmental basis for finding the disorders.
Alternative diagnostic methods during pregnancy
An ultra sound screening has higher sensitivity than Alpha fetoprotein diagnostic test and hence practitioners opt for a detailed ultrasound in the second trimester which do away with the need for conducting an alpha fetoprotein test.
Amniocentesis is an invasive procedure requiring insertion of needle into the uterus to collect the amniotic fluid and sampling the fluid for fetal proteins. This is done after 15 weeks of pregnancy. The invasive nature makes it uncomfortable for most women. The risk of miscarriage is usually higher with such invasive procedures
Related tests and procedures
In the triple test, AFP test is combined with analysis of hCG (human Chorionic Gonadotropin) and unconjugated estriol (a type of estrogen). When the concentration levels of another protein inhibin A is added to this test, it is known as Quad test. All these proteins are produced by the baby in the uterus. The test analyzes all the components together as an indicator to various disorders such as Down's syndrome, Edward's syndrome and other neural tube defects. These disorders result in severe intellectual disability. Both triple test and Quad test are suggestive only and require further procedures to establish the nature of the disorder.
How to reduce the risk of neural tube defects?
Since neural tube defects are the result of multiple factors such as diet, environment, genetics etc, the risk can be lowered by modifying these factors to a certain extent. For example, including more folic acid in diet for parents who had first NTD (neural tube defect) pregnancy lowers the chance for NTDs in second and consecutive pregnancies.
Alpha fetoprotein as a tumor marker
Alpha fetoprotein test is considered as a gold-standard to detect the presence of certain cancers such as cancer of ovaries, stomach, pancreas, liver etc in men, children and non pregnant women. High level of AFP is indicative of brain tumor, retinal cancer and lymphoma. Apart from acting as a tumor marker, recent researches have shown that AFP derived peptides act as tumor suppressing agents. AFP is also being studies for its use as a potential anticancer drug conjugate. AFP gene promoters are also being explored as a part of gene therapy for cancer.
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