A high alpha fetoprotein is not necessarily a bad thing, especially in patients with liver failure. If the alpha fetoprotein is high, it represents liver cell regeneration, suggesting that there is hope for the patient to regain life. Methemoglobin is synthesized by embryonic hepatocytes and gradually decreases from the serum about 2 weeks after the birth of the fetus. Methemoglobin in normal human serum is <20 μg/L (detected by ELISA). When there is a large number of hepatocyte necrosis, new hepatocyte regeneration or hepatocyte malignancy, rapid division and regeneration of tumor cells, the synthesis of methemoglobin increases and may show a rapid rise. If the high methemoglobin is caused by hepatocellular carcinoma, the methemoglobin level tends to keep rising and will only return to normal after taking treatment measures such as surgery, radiofrequency ablation or hepatic artery embolization chemotherapy. In case of recurrence of hepatocellular carcinoma, methemoglobin will also be elevated again. However, a high alpha fetoprotein in liver failure patients is not necessarily a bad thing. This is because a high AFP in liver failure indicates regeneration of liver cells, indicating that the patient's condition is improving, and the AFP usually decreases gradually as liver function improves. It should be noted that for primary hepatocellular carcinoma, only some patients have elevated serum methemoglobin while some patients have normal methemoglobin. Therefore, normal serum methemoglobin cannot exclude the possibility of having hepatocellular carcinoma, and it needs to be combined with the patient's medical history and imaging examination to make a comprehensive judgment. In addition, serum fetoprotein may also be elevated in cancers of the reproductive system, gastric cancer, pancreatic cancer, etc., which need to be combined with imaging and pathological examination for further differential diagnosis.