Skip to main content
. 2021 Apr 26;23(5):410–432. doi: 10.1177/1098612X211007071

Table 4.

Association of Veterinary Hematology and Transfusion Medicine (AVHTM) Consensus Working Group definitions of transfusion reactions

Transfusion reaction Definition
Acute transfusion reactions
Acute haemolytic transfusion reaction (AHTR) Acute, non-infectious, immunological or non-immunological reaction that occurs secondarily to accelerated destruction of transfused or recipient red blood cells (RBCs) and is characterised by acute haemolysis. AHTRs occur during or within 24 h of blood product administration. Causes of AHTRs can be divided into blood type incompatibilities and other causes of damage to transfused blood cells. Blood type incompatibilities are immunological acute haemolytic reactions (type II hypersensitivity reactions) due to major or minor incompatibilities between donor and recipient RBCs. A classic example would be in the case of a type A unit of blood given to a type B cat. Non-immunological causes of AHTRs may include thermal, osmotic, mechanical or chemical factors that damage transfused blood cells
Allergic reaction Acute immunological reaction that is secondary to a type I hypersensitivity response to an antigen within a blood product. This reaction occurs during or within 4 h of transfusion. It is characterised by clinical signs varying from transient and self-limiting to life-threatening anaphylaxis. Feline type I hypersensitivity reactions are typically respiratory (due to upper respiratory tract oedema, bronchoconstriction and excessive mucus production), although gastrointestinal signs and severe pruritus can also occur
Febrile non-haemolytic transfusion reaction
(FNHTR)
Acute non-immunological or immunological reaction characterised by a temperature >39°C (102.5°F) and an increase in temperature of >1°C (1.8°F) from the pre-transfusion body temperature, during or within 4 h of a transfusion, where external warming, underlying patient infection, AHTR, TRALI (see below) and TTI (see below) have been ruled out
Transfusion associated circulatory overload (TACO) Acute, non-immunological reaction that is secondary to an increase in blood volume mediated by blood transfusion, characterised by acute respiratory distress and hydrostatic pulmonary oedema. This reaction occurs during or within 6 h of transfusion. It is associated with clinical, echocardiographic, radiographic or laboratory evidence of left atrial hypertension or volume overload. These patients typically have a positive response to diuretic therapy
Transfusion associated lung injury (TRALI) Acute, immunological reaction that is secondary to antigen–antibody interactions in the lungs. TRALI is characterised by acute hypoxaemia with evidence of non-cardiogenic pulmonary oedema on thoracic radiographs, during or within 6 h of allogenic blood transfusion. Patients diagnosed with TRALI have no prior lung injury, no evidence of left atrial hypertension and no temporal relationship to an alternative risk factor for acute respiratory distress syndrome (ARDS)
Transfusion associated dyspnoea (TAD) Acute transfusion reaction characterised by the development of acute respiratory distress during or within 24 h of the end of a transfusion where TACO, TRALI, allergic reaction and underlying pulmonary disease have been ruled out
Hypotensive transfusion reaction Acute, non-immunological reaction that is secondary to the infusion of stimulators of vasodilation and hypotension. It is characterised by the rapid onset of significant hypotension during or shortly after the completion of a transfusion, in the absence of other causes of hypotension, and improvement with cessation of the infusion. There is usually a decrease in systolic blood pressure of at least 30 mmHg from baseline
Citrate toxicity Acute, non-immunological reaction that is secondary to the transfusion of a large volume of blood with citrate as the anticoagulant, and is characterised by a significant systemic hypocalcaemia within hours of initiating the transfusion
Hyperammonaemia Acute, non-immunological reaction that is secondary to hyperammonaemia and characterised by signs of development of encephalopathy (neurological signs such as ataxia, head pressing, circling, seizures and vomiting), during or immediately after (minutes to a few hours) blood transfusion of stored blood or stored blood components. It is a potentially life-threatening reaction in patients with liver disease (liver failure, portosystemic shunt) or in premature neonates with an immature functioning liver, which are unable to metabolise and excrete ammonia properly
Acute-to-delayed transfusion reactions
Transfusion transmitted infection (TTI) Acute or delayed, non-immunological reaction secondary to the transfusion of pathogen-contaminated blood or blood components. TTI can occur hours to years after the transfusion due to the presence of the infectious agent in the blood/blood component unit collected from an infected donor, or from pathogen contamination of blood/blood component units during processing, storage or transfusion. Clinical signs are highly dependent on the pathogen transmitted and its pathogenicity for cats, and the clinical status of the recipient
Transfusion-associated graft vs host disease (TAGVHD) Acute to delayed, immunological reaction that is secondary to donor lymphocytes engrafting on and eventually attacking host tissue. TAGVHD occurs 48 h to 6 weeks following transfusion and has a high mortality rate in human patients (>90%). The reaction is characterised by a skin rash, diarrhoea, fever, hepatic dysfunction and bone marrow hypoplasia. Liver and skin histopathology have a characteristic appearance. In humans, it is most common in immunocompromised individuals or when special circumstances cause transient immunosuppression
Delayed transfusion reactions
Delayed haemolytic transfusion reaction (DHTR) Delayed, non-infectious, immunological or non-immunological reaction that occurs secondarily to lysis or accelerated clearance of transfused RBCs. Delayed haemolytic transfusion reactions occur 24 h to 28 days after blood product administration. Immunological DHTRs are typically caused by a secondary immune response to the donor’s RBCs. Non-immunological DHTRs occur due to thermal, osmotic, mechanical or chemical factors that damage transfused blood cells, causing delayed haemolysis
Delayed serological transfusion reaction (DSTR) Delayed, immunological reaction that is secondary to the development of new, clinically significant antibodies against the transfused product without evidence of haemolysis. DSTRs occur 24 h to 28 days after a transfusion 24
Post-transfusion purpura (PTP) Delayed, immunological reaction that is secondary to alloimmunisation against platelet antigens. PTP is characterised by thrombocytopenia arising 5–12 days following transfusion of any platelet-containing blood product

Reproduced with permission from the AVHTM 98