Hemolysis is a clinical entity, which can be severe. It is commonly of multifactorial etiology. The activity of a specialist in transfusion medicine consists in treating the patient with transfusion support in case of severe anemia. If the etiology is partly alloimmune this therapeutic strategy is more arduous. Immunohematological work-up must be very rigorous to ensure transfusion management with utmost safety. However, without the precise knowledge of both the clinical condition and the treatment (current and past) of the patient, such management is impossible.