Occasionally, we encounter a patient with hepatitis B or C who has no previous history of hepatitis B or C, but has a history of surgery or blood transfusion, and no other means of transmission have been ruled out. Could it be that the blood transfused by the hospital was faulty and the blood had not been tested before? Trauma, childbirth, surgery and other situations require blood or other blood products to be transfused. The blood and blood products in hospitals are strictly checked and tested and will ensure their safety, which we cannot doubt. But do we have to let our guard down? No. I would only recommend blood or blood product transfusions if necessary. This is because there are also some potential risks associated with blood transfusion, what is this potential risk? In the city, there are many fixed blood donation points and mobile blood donation vans to facilitate blood donation. Hospitals also provide blood donation windows, and those who have a heart will donate blood according to their situation. Once this blood enters the blood bank, it is tested, first by centrifugation into serum and red blood cells, and then by blood type testing, transaminase testing, enzyme-linked immunoassay testing, and nucleic acid testing. But the methods and techniques used in these routine blood tests detect antibodies (such as hepatitis C anti-HCV) or antigens (such as hepatitis B HBsAg) to the virus, not the virus itself. Some people are infected with the virus and it takes time for the virus to enter the body before antibodies are produced, the time period from infection to antibody production is the “window period”. If the blood donor is in the antibody window period, there is already a virus in the blood, he went to donate blood, the blood transfusion to others, the transfusion rate should be 100 percent. The blood station has done antibody screening in strict accordance with the national regulations, but because the infection occurs during the antibody window period, the blood station is not in violation of the national regulations. The most common diseases with a window period are: Hepatitis B, Hepatitis C, AIDS, etc.. They have different lengths of window periods. As medicine progresses, the “window period” is getting shorter. Hepatitis B, hepatitis C and AIDS have been shortened from 50 days, 72 days and 22 days to 25 days, 59 days and 11 days now. If a person is infected with such a virus and donates blood during the “window period”, the virus cannot be detected, but at the same time, the virus is most infectious during this period, which means that the donor has good intentions, but does something bad by mistake and transmits the disease to the recipient. The risk of blood transfusion during the “window period” cannot be eliminated, so how can we reduce this risk? In the case of hepatitis B virus, if we get the hepatitis B vaccine in time and test regularly for antibodies, we will avoid reinfection with hepatitis B. For newborns, the timing of hepatitis B vaccination is: the first dose of hepatitis B vaccine within 24 hours of birth; the second dose when they reach 1 month; and the third dose when they reach 6 months. Before receiving the hepatitis B vaccine, appropriate tests must be performed, and liver function and hepatitis B five items are routinely tested. The principle of vaccination is that only those who have normal liver function and all five items of hepatitis B are negative should receive the full course (three doses) of hepatitis B vaccine. If the “hepatitis B surface antibody” test is positive before the hepatitis B vaccination, no further vaccination is required. If the “hepatitis B surface antibody” is weakly positive, then a booster shot is required. Therefore, blood or blood products transfusion is risky for the recipient, and it is recommended that you only transfuse if your doctor recommends that it is necessary, otherwise you run the risk of being infected by the “window period” virus that is hidden in the “normal blood”, so transfusion should be done with caution. Therefore, blood transfusion should be done with caution. It is important to know more about medical knowledge in order to better guide us to protect our health.