Acute haemolytic transfusion reactions (AHTR) are characterised by fever, a fall in haemoglobin (Hb), rise in bilirubin and lactate dehydrogenase (LDH) and a positive direct antiglobulin test (DAT). They generally present within 24 hours of transfusion.
Delayed haemolytic transfusion reactions (DHTR), occur more than 24 hours following a transfusion and are associated with a fall in Hb or failure to increment, rise in bilirubin and LDH and an incompatible crossmatch not detectable pre transfusion.
Hyperhaemolysis (HH) is characterised by more severe haemolysis than DHTR, with haemolysis affecting the transfused red cells and the patient’s own red cells; there is a decrease in Hb to below pre-transfusion levels, which is often associated with a reticulocytopenia. It may be triggered by a new red cell alloantibody, but frequently no new red cell antibody is identified. Hyperhaemolysis can be divided into acute and delayed hyperhaemolysis.
SHOT has collected data on haemolytic transfusion reactions (HTR) since 1996. Until 2006, this category only included delayed HTR, as acute reactions were reported under the ATR category. Alloimmunisations are not included within the numbers in the figure above.