In 1956, it was found that the serum of patients with primary hepatocellular carcinoma and that of fetuses had a special component in common, AFP (short for “alpha-fetoprotein”), which is a kind of glycoprotein measuring the immunity strength of liver tumors, just like gammaglobulin and preprotein. AFP, like C-globulin and preprotein, is a glycoprotein that measures the strength of liver tumor immunity, and is present in very small amounts in normal human serum. AFP is a protein produced by hepatocytes and ovarian xanthoblasts during the embryonic period, which disappears one week after birth and gains the ability to synthesize this protein when the hepatocytes become cancerous (called the reentry phenomenon). It is also produced in large numbers of newborn hepatocytes. The role played by AFP in the fetal period is still not well understood and may lie mainly in maintaining a normal pregnancy and keeping the embryo from being rejected by the mother. Prior to 1970, AFP was mainly detected by two-way agar diffusion, which had a low positive rate (insufficient sensitivity) but a high specificity for the diagnosis of primary hepatocellular carcinoma. sensitive assays have been developed since 1971, and their positive rates have increased significantly. Currently, enzyme labeling method, enzyme labeling electrophoresis method and radioimmunoassay are commonly used for detection. The normal value of radioimmunoassay is <20ug/L. Clinical data show that about 40% of chronic hepatitis have elevated AFP, about 60% of cirrhosis have elevated AFP, and more than 95% of liver cancer patients have elevated AFP. This indicates that as the severity of liver disease increases, the proportion of AFP elevation also increases substantially. AFP is a specific tumor marker for the diagnosis of primary liver cancer, which has the functions of establishing diagnosis, early diagnosis and differential diagnosis. It is the most sensitive and specific indicator for early diagnosis of primary liver cancer, and as an indicator of cancer, there is no accurate rate that can exceed AFP. The elevation of AFP in the serum of primary liver cancer patients can be tens of times or even tens of thousands of times that of normal people. In addition to AFP-negative hepatocellular carcinoma, if AFP is less than 20ug/L, primary hepatocellular carcinoma can be basically ruled out; those between 100 and 300ug/L must be followed up and the dynamic change of AFP must be closely observed, so as to pay attention to possible small hepatocellular carcinomas; if AFP is more than 400ug/L or lasts for 4 weeks and is more than 200ug/L, hepatocellular carcinomas are very likely, and CT and other imaging examinations should be carried out further. Dynamic observation of AFP levels can detect hepatocellular carcinoma 8 months or more before the onset of symptoms and can distinguish it from other false-positive cases. Dynamic or regular examination of AFP in liver cancer patients can help to understand the progression of the disease. the level of AFP can reflect the size of the tumor, and the rising level suggests deterioration of the disease. Usually, AFP decreases after surgical resection of hepatocellular carcinoma (it should be reduced to below 20ug/L), if it does not decrease much, it suggests that the resection is not complete; if the tumor shrinks and AFP rises, it indicates that the tumor metastasizes or spreads. The prognosis of those whose AFP drops to less than 20ug/L after tumor resection is significantly better than those whose AFP does not drop to normal. Cholangiocarcinoma, highly differentiated and lowly differentiated hepatocellular carcinoma and tumor necrosis liquefaction can be negative for AFP, because highly differentiated hepatocellular carcinoma cells rarely produce or do not produce AFP, and very poorly differentiated hepatocellular carcinoma cells do not produce AFP either, and it is mainly the moderately differentiated hepatocellular carcinoma cells that synthesize AFP. metastatic hepatocellular carcinomas are very seldom elevated. In contrast, AFP is elevated in many non-cancerous liver diseases. In other words, low AFP does not necessarily mean no cancer, and high AFP does not necessarily mean cancer. In non-cancerous liver disease, most of the AFP level is below 500ug/L, and it is transient. In general, AFP is elevated in about 10% of viral hepatitis patients, 20% to 40% of chronic hepatitis patients with marked inflammatory activity have elevated AFP, and 85% of patients recovering from fulminant hepatitis have elevated AFP, suggesting that the range of elevated AFP has prognostic significance. Multiple dynamic tests should be performed to differentiate hepatocellular carcinoma in patients with low-level elevated AFP liver disease, especially those with 50-400ug/L. Generally, the AFP level decreases or normalizes with the improvement of acute liver disease, decreases or continues to be low in cirrhosis, and gradually increases in hepatocellular carcinoma. Some patients with cirrhosis have AFP in the thousands for a long time, but there is no sign of hepatocellular carcinoma for many years. In cases of chronic hepatitis and cirrhosis, AFP and ALT (serum alanine aminotransferase) are synchronized, and most of them decrease with the improvement of the disease in l~2 months. In addition, in the diagnosis of congenital diseases, the significance of detecting the level of AFP in amniotic fluid has attracted attention, and the level of AFP in the amniotic fluid of anencephalic infants is significantly elevated. Congenital nephropathy and spina bifida, hydrocephalus, dodecal and esophageal atresia, renal degeneration, intrauterine asphyxia, preeclampsia, and twin births have been similarly reported. Therefore, detection of AFP levels in amniotic fluid can help in the prenatal diagnosis of certain congenital disorders. Elevated serum AFP has also been seen in teratomas, testicular and ovarian tumors.