The aim of this paper is to describe the generalized transfusion, blood type blood type, blood products, and patient safety when preparing blood products. Because of the simplicity of the use of blood products, transfusion therapy is considered one of the simplest treatment methods, but in biological terms, considering the origin and composition of blood products, it is one of the more complex medical procedures that should be understood as tissue transplantation. One of the potential problems is the formation of blood groups, of which there is little, but a time of inadvertence to avoid a transfusion reaction is sufficient. The ABO system of blood groups is also the most important first discovered blood group system. In the ABO system of blood groups there are two antigens: A and B antigens. The four basic blood groups of the ABO system are: A, B, AB and O. Other importantly, the blood system is the Rh system. Up to now, 51 antigens have been detected in this system, but there is enough knowledge of five antigens of this system, namely: C, C, D, E and E. A routine anti D serum detects D antigen. So we differentiate RhD positive and RhD negative. Blood transfusions are also useful for blood transfusions, intended for the prevention or treatment of various diseases. From one dose of blood most often four blood preparations are obtained. We differentiate erythrocyte, platelet, leukocyte and plasma concentrations. From them we can get a number of blood products because the patient can only be treated with the missing blood components. Each medical procedure possesses a certain risk, including transfusion therapy. Equal blood tests are applied in Croatia and are equally prepared for blood preparations as in Western European countries for which various organizations are responsible.