Why is blood testing done before donating blood?

The blood collection staff at the blood station or relevant personnel from the hospital will communicate with you first and ask whether you have any infectious diseases, high blood pressure, hypoglycemia, whether the liver and kidney functions are normal, whether the heart is normal, etc., and You will be asked to fill out a "physical condition registration form" or a questionnaire. After meeting the requirements, a blood sample will be taken (usually a drop of blood from your fingertip) to determine the blood type and other aspects. Then the blood donor will be collected and based on the Blood type: The donor's blood (usually 200ml or 400ml per blood donation) is individually labeled with blood type and other relevant information and then classified and stored. After the blood collection work is completed, the blood center will test all the collected blood again, and the blood that meets the blood supply safety requirements will be put into the blood bank for refrigerated storage. If it is found during the test that the blood does not meet the requirements, it may be scrapped. Even if the blood contains some kind of virus or infectious agent, the blood center will generally search for the blood donor through the personal information filled in when donating blood, so as to notify the blood donor or take measures. Relevant effective measures to prevent infection.