Alpha-fetoprotein (AFP) is a glycoprotein present in human serum, derived from early fetal hepatocytes and yolk sac, and is generally detectable in fetal serum at about 4 weeks of gestation. Meanwhile, AFP is also considered as a serum marker of primary liver cancer, which is also closely related to the occurrence and development of other tumors and can be used to examine: 1. Primary liver cancer: AFP is a specific marker of primary liver cancer, which can be used for the screening and diagnosis of liver cancer, as well as to judge the treatment effect and predict recurrence. If AFP > 400ng/ml, it can be used as one of the diagnostic criteria for liver cancer after excluding pregnancy and germinal germ tumor. If AFP gradually increases and does not decrease, or >100ng/ml for 8 weeks, imaging and liver function tests need to be improved to confirm the diagnosis of the presence of hepatocellular carcinoma. About 30% of patients with hepatocellular carcinoma can maintain normal AFP level, so the diagnosis rate can be improved by detecting AFP heterogeneous body. Meanwhile, positive AFP-L3 after surgery indicates high residual carcinoma or recurrence rate and metastasis rate, as well as poor prognosis. If AFP-L3 is not reduced to less than 10% or is elevated again, it suggests the possibility of recurrence; 2. Down syndrome: pregnant women are usually screened for serum markers before delivery, and AFP is one of the serological indicators for screening Down syndrome , which can be used to assess the risk of fetal disease during pregnancy; 3. Other aspects: other liver diseases include hepatitis B, acute hepatitis, chronic hepatitis, cirrhosis, and severe hepatitis Active hepatocyte regeneration may also be accompanied by elevated AFP. There are also germ cell tumors, embryonal tumors of the testes or ovaries, etc., which can also present with elevated AFP.