Alpha fetoprotein

Abstract

Results of the authors' own experiences and of data from the literature are summed up. Among purification methods, the use of immunoadsorbents fulfills the strictest requirements for purity. The physiochemical properties of alphafetoprotein (AFP) are mentioned. The authors' own method of radioimmunoassay (RIA) is described briefly. They found AFP to be the inhibiting agent in RIA; adults were found to be more tolerant to homologous AFP, but this tolerance can be broken by immunization with the heterologous analog of the antigen or with chemically modified homologous AFP. AFP has an established role in monitoring primary liver cancer and testicular teratocarcinoma values exceeding 5 μg/ml were found in 23 of 42 primary liver cancer cases; the high values found sometimes in hepatitis and in the regeneration stage of cirrhosis are transient. AFP values in fetal material are highest during the 14th gestational week, and decrease after the 32nd week; higher values are found in Rh immunization, diabetes, ataxia teleangiectasia and neonatal hepatitis, lower values in toxemia of pregnancy. Also maternal serum levels of AFP are highest in the 2nd trimester, which is evidence of their fetal origin and of feto maternal transfer. In hydatidiform mole and choriocarcinoma levels are normal, which may be used in the differential diagnosis against pregnancy. In bleeding during early pregnancy, high levels in the uterine contents point to contamination with fetal elements, low levels show that the bleeding is mainly of maternal origin. For the same reason are levels higher in premature separation of the placenta than in placenta praevia. In legal abortion the level rises during the abortion. In threatened abortion levels are lower, but not sufficiently to be informative, than in normal pregnancy; high levels are found with fetal malformation or fetal death. Also in high risk late pregnancies are high levels often associated with fetal complications. In the amniotic fluid, AFP tracings resemble those in the fetus; in late pregnancy they may even be used for an estimation of the gestational age. High levels are found in the 'open' type of neural tube defects, resulting from CSF leakage, transudation from fetal capillaries and failure of deglutition, since fetal AFP levels are normal in these cases. Detection efficiency is 75% for spina bifida (higher before 24 weeks) and 94% for anencephaly. Other conditions showing high values are Rh immunization congenital nephrosis, congenital esophageal atresia, hydrocephalus etc. The risk and some technical details of amniocentesis are discussed, but it cannot be used for the screening of neural tube defects, since 90% of the cases occur without any past history; however, screening by determining maternal serum levels of AFP seems promising (if cases with twin pregnancy are excluded); high levels would indicate amniocentesis. The practical implications of such a screening program are discussed. Finally, as for the methods for estimating AFP levels, the authors definitely prefer radioimmunoassay, but admit that some technical difficulties still have to be overcome.