Indications for blood transfusion need to be analyzed according to the missing blood components and the degree of deficiency. Common indications such as hemoglobin <60g/L, white blood cell count <1.0*10^9/L, or coagulation factor deficiency with severe bleeding are recommended to consult a specialist. 1. Red blood cell transfusion: all kinds of acute and chronic anemia, often applied to hemoglobin <60g/L or hematocrit <0.2, depending on age and compensation. Commonly used suspension of red blood cells, less leukocyte red blood cells. 2. Platelet transfusion: the indications for therapeutic transfusion, there are thrombocytopenia caused by platelet generation disorder, dilution thrombocytopenia, bleeding caused by abnormal platelet function. There is no standardized indication for prophylactic transfusion, and it is generally considered that PLT＜20*10^9/L with infection, fever, splenomegaly, etc., PLT＜10*10^9/L with stable condition, no fever, bleeding, etc., and PLT＜5*10^9/L, with or without bleeding. 3. Plasma transfusion: it is mostly applied to patients with multiple coagulation factor deficiencies accompanied by severe bleeding, and is also used for those with massive bleeding, or abnormal coagulation test and needing invasive operation, such as those with coagulation factor deficiencies other than Factor V and VIII, severe trauma, DIC, and so on. Blood resources are more scarce, usually saline or balanced salt solution will be used for rehydration, and those who need blood transfusion need to strictly follow the doctor's instructions for transfusion.