Alpha fetoprotein in the blood

Alpha-fetoprotein is an a-glycoprotein normally synthesized in the yolk sac of the embryo and then by the liver of the fetus. The level of alpha-fetoprotein is elevated in newborns and, consequently, in pregnant women. The content of alpha-fetoprotein decreases rapidly during the first year of life, reaching the level typical for adults by the age of 1 year (normally < 20 ng/ml).

Reference values of alpha-fetoprotein in blood serum: adults - up to 10 IU/ml; in women in the II-III trimester of pregnancy - 28-120 IU/ml; newborns in the first day of life - up to 100 IU/ml. Half-life - 3-6 days.

Elevations (>500 ng/mL) detected in high-risk patients (eg, liver mass detected on ultrasonography) are diagnostic of primary hepatocellular carcinoma (HCC), although not all hepatocellular carcinomas produce alpha-fetoprotein.

Determination of alpha fetoprotein content in serum is used:

• for diagnosis and monitoring of treatment of hepatocellular cancer;
• for the diagnosis of germ cell tumors;
• for the diagnosis of metastases of any tumor to the liver;
• for screening in high-risk groups (liver cirrhosis, hepatitis, α ₁ -antitrypsin deficiency );
• for prenatal diagnostics (malformations of the neural canal, Down syndrome in the fetus);
• to assess the degree of maturity of the fruit. [ 1 ], [ 2 ]

Causes of increased alpha-fetoprotein

Because small tumors may have low AFP levels, elevated AFP levels suggest the possibility of hepatocellular carcinoma. However, the degree of AFP elevation has no prognostic value. In populations with high rates of chronic hepatitis B and hepatocellular carcinoma (e.g., sub-Saharan Africa, ethnic Chinese), AFP may reach very high values (e.g., 100,000 ng/mL), whereas lower values (approximately 3,000 ng/mL) are found in areas with lower tumor incidence.

Some other diseases (eg, embryonal teratocarcinoma, hepatoblastoma, some liver metastases from gastrointestinal tumors, some cholangiocarcinomas ) cause AFP levels of 500 ng/mL. In fulminant hepatitis, AFP may occasionally rise to 500 ng/mL; lesser elevations occur in acute and chronic hepatitis. These elevated values probably reflect liver regeneration. Thus, the sensitivity and specificity of AFP vary considerably among populations, but values of 20 ng/mL occur with frequencies of 39 to 64% and 76 to 91%, respectively. Because AFP levels < 500 ng/mL are nonspecific, 500 ng/mL is used as the diagnostic cutoff.

Alpha-fetoprotein as an oncomarker has the following clinical applications: firstly, to detect and monitor primary hepatocellular carcinoma, which usually occurs in liver cirrhosis; secondly, to detect testicular teratoblastoma and, thirdly, to assess the effectiveness of therapy for these diseases. An increase in the concentration of α-fetoprotein in hepatocellular liver cancer in 50% of patients is detected 1-3 months earlier than clinical signs of the disease appear. In primary liver carcinoma, the concentration of alpha-fetoprotein in the blood is more than 15 IU/ml is detected in 95% of cases (15-100 IU/ml - in 12%; 100-1000 IU/ml - in 14%; 1000-10,000 IU/ml - in 29%; 10,000-100,000 IU/ml - in 39% of cases). In metastatic liver damage, the concentration of α-fetoprotein is more than 15 IU/ml is detected in 9% of cases (15-100 IU/ml - in 7%; 100-1000 IU/ml - in 2%).

The alpha-fetoprotein content correlates well with the effectiveness of chemotherapy treatment of carcinoma (a significant decrease indicates therapeutic effectiveness). Due to the fact that the full effect of chemotherapy is usually absent, normalization of the alpha-fetoprotein level in the blood of patients is not observed. Tumor removal is accompanied by a sharp decrease in the alpha-fetoprotein content in the blood, its persistent increase indicates the non-radical nature of surgical treatment.

Alpha-fetoprotein - a method of prenatal examination of pregnant women

In the second trimester of pregnancy, if the fetus has Down syndrome, the concentration of alpha-fetoprotein in the pregnant woman's blood serum is reduced, and the concentration of chorionic gonadotropin is increased. Taking this into account, the study of alpha-fetoprotein and chorionic gonadotropin is used as a method of mass prenatal examination of pregnant women, with the help of which it is possible to identify a high-risk group for the presence of fetal malformations or Down syndrome.

Serum alpha-fetoprotein median concentration values for screening of congenital malformations in the second trimester

Pregnancy period	Medians for AFP, IU/ml
15	32
16	34
17	36
18	40
19	45
20	49

Hereditary diseases accompanied by changes in AFP concentration

Increased concentration	Decreased concentration
Fetal neural canal malformations Fetal hydrocephalus Congenital esophageal atresia Tetralogy of Fallot Lipoid nephrosis of the fetus	Down syndrome

[ 3 ], [ 4 ], [ 5 ], [ 6 ], [ 7 ]