**Abstract**

Haemolytic post-transfusion reaction is caused by accelerated destruction of erythrocytes by immunological incompatibility between the donor and the recipient. It also occurs for non-immunological reasons: thermal, osmotic or mechanical damage and bacterial infection. Haemolysis can be endogenous (usually acute) and exogenous with macrophages in the reticuloendothelial system of spleen or liver (delayed). The pathophysiology: antibody binding erythrocyte antigens, antibody-coated erythrocytes interaction with monocytes/macrophages activating phagocytosis or antibody-dependent cytotoxicity and the production of inflammatory mediators. Antibodies destroying transfused blood cells are called clinically relevant antibodies that are active in vitro at 37°C. An interesting mechanism is the "bystander immune cytolysis".

**Keywords:** haemolytic reaction, haemolysis, transfusion reaction, HTR
