Plus-Hex CLINICAL
Types of reaction
Typical clinical signs of transfusion reactions include the following [ 2, 13 ]:
• Tachycardia( but a cat with shock could be bradycardic)
• Arrhythmias
• Hypotension and weak peripheral pulses
• Tachypnoea
• Dyspnoea
• Pale mucous membranes
• Weakness, lethargy, decreased mentation
• Muscle tremors
• Evidence of haemolysis, e. g. jaundice, haemoglobinuria, haemoglobinaemia
• Pyrexia
• Vomiting / diarrhoea
• Facial oedema.
Transfusion reactions are classified as acute and delayed reactions. Acute onset can occur at the start of or during the transfusion, whereas delayed responses can occur days to weeks after the transfusion [ 2 ].
Acute immunological transfusion reaction
An acute immunological transfusion reaction, also known as a type I hypersensitivity reaction, is a reaction to an antigen within the transfused blood product and is mediated by immunoglobulin E( IgE) [ 2 ]. This response releases inflammatory mediators, such as histamine, which causes an acute inflammatory response( hives, facial swelling, vomiting, diarrhoea and pyrexia). These reactions normally occur within 4 hours, and are predominantly seen within the first hour of transfusion. In more severe cases, patients may develop anaphylaxis and could show haemodynamic collapse with hypotension, with clinical signs such as hypersalivation, dyspnoea and eventual collapse.
Acute haemolytic transfusion reaction
An acute haemolytic transfusion reaction( AHTR) occurs within 24 hours of the transfusion and may happen when a recipient already has antibodies to the donor RBC antigens. This reaction results in the transfused RBCs being destroyed by the recipient ' s immune system [ 2 ]. An AHTR can be accompanied by a type I hypersensitivity reaction, which further compromises oxygen delivery. Haemolysis can be accompanied by clinical signs of pyrexia, vomiting, diarrhoea, DIC, haemoglobinaemia and haemoglobinuria.
Delayed haemolytic transfusion reaction
A delayed haemolytic transfusion reaction( DHTR) occurs after 24 hours and up to 28 days after a transfusion, and involves haemolysis of the transfused RBCs. Patients with this reaction will display signs of anaemia, mild jaundice and pyrexia due to a severe drop in PCV.
Both AHTR and DHTR can largely be avoided by appropriate blood typing and cross-matching [ 13 ].
Febrile non-haemolytic transfusion reaction
Febrile non-haemolytic transfusion reactions involve the haemolysis of transfused RBCs days to weeks after the transfusion and are an immune reaction to transfused leukocytes and cytokines. Patients will develop a severe drop in PCV, resulting in clinical signs such as anaemia, mild jaundice, pyrexia and nausea, which can be apparent from hypersalivation and vomiting. As the white blood cells deteriorate, they release inflammatory molecules, resulting in the febrile reaction [ 13 ].
Xenotransfusions in cats
A xenotransfusion( transfusion of blood from another species, e. g. the dog) can be considered in the absence of an available or suitable feline donor; however, there are many associated risks and as a result it is usually considered as a last resort. Xenotransfusions should be considered only in a cat that is clinically showing decompensation and inadequate oxygen delivery even with supportive oxygen supplementation [ 17 ].
In hypoxic patients, xenotransfusions can improve the clinical signs in the short term to help stabilise the patient while a suitable feline blood donor is located. If anaemia is regenerative, xenotransfusion may be beneficial by temporarily improving the clinical signs while the patient regenerates their own supply of RBCs [ 18 ].
The benefits of xenotransfusion in feline patients are short-lived; most transfused RBCs are haemolysed within 4 – 7 days [ 11, 17 ]. Patients with severe blood loss or non-regenerative anaemia will require additional blood transfusions, and the risk of a transfusion reaction increases with each transfusion received.
Cats with a history of a prior xenotransfusion are not suitable candidates to receive subsequent xenotransfusions, as prior exposure to canine blood can lead to immune sensitisation, triggering an autoimmune response and the development of a fatal reaction, anaphylaxis or delayed haemolysis [ 2 ].
Xenotransfusions should be considered as a last resort in a life-threatening emergency as cats may already carry antibodies to canine RBCs, which can cause a fatal transfusion reaction even at the first transfusion [ 19 ].
Volume 41( 3) • June 2026
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