Alpha-fetoprotein

• OMIM: 104150
• UniProt: P02771

Alpha-1 -fetoprotein (AFP), and Alphafoetoprotein or α1 - foetoprotein, is a glycoprotein in mammals which is formed during human embryonic development during pregnancy from endodermal tissue, and in fetal liver, or adult, in particular in tumor cells of the liver. Physiologically alpha -1 -fetoprotein has the function of a fetal transport protein, in particular the transport of copper, nickel, fatty acids and bilirubin in fetal blood plasma.

AFP is structurally closely related to the transport protein albumin, vitamin D binding protein and afamin. Production begins in the fourth week old embryo is highest in the twelfth to sixteenth week and almost completely stops after birth. In adults, the plasma level is usually less than 40 ng / ml.

Applications

Very high AFP concentrations in the maternal blood or amniotic fluid are considered indicators closure defects of the unborn child. These include abdominal wall defects such as omphalocele and gastroschisis, and the neural tube defects such as spina bifida and anencephaly. In males and non -pregnant women, high AFP concentrations on an active hepatitis, liver cirrhosis and hepatocellular carcinoma ( hepatocellular carcinoma, HCC) point. Low levels of AFP are 14 to 20 weeks of pregnancy as an indication of Down syndrome ( trisomy 21) in the unborn child.

Laboratory tests

Pregnancy

In the serum

The measurement of serum AFP concentration in pregnancy may be requested as an isolated laboratory study. The determination of the serum AFP value can be carried out in combination with other serum values. Then it is a part of prenatal screening tests such as the so-called triple test or the quadruple test.

In Germany medical guidelines for serum AFP values ​​were published. According to them, values ​​are more than 2.5 MoM as an indication of a closure defect. As a recommendation, a detailed ultrasound examination and the patient's request amniocentesis to investigate the AFP and AChE in amniotic fluid is then proposed. Serum AFP values ​​between 2.0 and 2.5 MoM be the norm values ​​in the borderline range in which a targeted ultrasound examination can be offered.

As sources of error in the interpretation of the measured AFP values ​​apply: miscalculation of gestational age, failure to take account of the maternal body weight, disregarding the smoking status and failure to take account of the ethnic origin of the examined patient. In particular, pregnant women of African descent have significantly higher serum AFP values ​​than women of European origin. It must also be borne in mind that the AFP concentrations are elevated in women with twin pregnancy twice average that violations of the placenta ( bleeding, Placentahämatome ) can lead to the AFP increase in maternal serum, and that extremely high levels of AFP in Scandinavians on a Finnish may indicate: - ( Finnish type nephrotic syndrome syn. ) nephrosis.

In amniotic fluid

The amniotic fluid AFP level is usually also measured in Germany in each amniotic fluid sample to search for neural tube defects, even in otherwise indication for amniocentesis. An elevated AFP level in the amniotic fluid is considered as well as in serum not as proof of the existence of a neural tube defect or other closure defects. As proof applies only proof of the defect on ultrasound. In combination with the AFP value and the acetyl- cholinesterase (AChE ) is often studied in the amniotic fluid. A positive AChE value is valid in combination with an elevated AFP level, a clear reference to a neural tube defect in the fetus.

No generally accepted limits for the AFP made ​​in Germany in the amniotic fluid. Usually, this limit defines each laboratory itself, it relies on appropriate references from publications that suggest such limits. As one of the most important publications in this context applies the UK Collaborative Study on Alpha-fetoprotein in Relation to Neural -tube Defects. According to this study, the threshold for elevated AFP concentrations during pregnancy changed stepwise. Between the 13th and 15th week, the limit should be 2.5 MoM, 16 to 18 weeks at 3.0 MoM, 19 to 21 weeks at 3.5 MoM, and between the 22. , and 24 weeks at 4 MoM.

As sources of error in the interpretation of the measured levels of AFP are: Bloody amniotic fluid (contamination with fetal erythrocytes) often leads to increased AFP values ​​, puncture after amnioinfusion leads to extremely low AFP values

Tumor markers

AFP serves as a marker for following tumors:

• Germ cell tumors of the testis and ovary
• Yolk sac tumor
• Hepatocellular carcinoma (HCC )