Alpha-fetoprotein is a glycoprotein. Under normal circumstances, this protein comes mainly from the liver cells of the embryo and disappears from the bloodstream about two weeks after birth, so that the amount of AFP in the serum of a normal person is still less than 20 micrograms per liter. However, when hepatocytes become cancerous, the function of producing this protein is restored. Therefore, if significantly higher levels of alpha-fetoprotein can be detected in the blood, the possibility of liver cancer should be considered. Methemoglobin was initially used for early diagnosis of liver cancer. It can be elevated 8 months before the appearance of symptoms of liver cancer, when most patients with liver cancer are still asymptomatic and the tumor is small, and the prognosis of these patients is significantly improved after surgical treatment. Nowadays, alpha-fetoprotein is also widely used in monitoring the efficacy of liver cancer surgery, postoperative follow-up and follow-up of high-risk groups. However, AFP is also elevated in women with normal pregnancy, in a few cases of hepatitis and cirrhosis, and in gonadal malignancies, but not as much as in hepatocellular carcinoma. These conditions should be excluded when using methemoglobin to diagnose hepatocellular carcinoma. In addition, some hepatocellular carcinomas may have normal AFP values, so imaging tests should be performed at the same time to increase the diagnostic reliability.