Alpha-fetoprotein is a glycoprotein in the human body, which is found mainly in liver cells during the embryonic period. After the fetus is born for 2 weeks, the level of alpha-fetoprotein disappears from the blood, so the level of alpha-fetoprotein in normal people is less than 20 μg/L. When the liver cells become cancerous, the function of producing protein is restored again. When the condition deteriorates rapidly, the level of alpha-fetoprotein will rise sharply, so alpha-fetoprotein is used as a specific indicator for diagnosing primary liver cancer in clinic. However, alpha-fetoprotein does not mean liver cancer, because acute and chronic hepatitis, cirrhosis and digestive tract cancer can also cause alpha-fetoprotein to rise, so clinical diagnosis needs to be combined with imaging examination.