Companion May 2012 - BSAVA

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How to select and collect: feline blood donation 16 | companion Danielle Banks, Diagnostic Supervisor at Davies Veterinary Specialists, describes the practicalities of feline blood donation Blood transfusions may be carried out for a variety of conditions, including those associated with anaemia (haemorrhage, haemolysis, or reduced erythropoiesis), coagulopathies, sepsis, disseminated intravascular coagulation and specific factor deficiencies. Unfortunately the methods of collection for feline blood do not make it suitable for storage nor, at present, is feline blood available from external blood banks. Therefore, when presented with a case requiring a transfusion it is best practice to collect blood at the time of need specifically for that case. Feline blood types The feline blood AB type system is quite different to that of the dog. There are three blood types; type A, type B and type AB (which is rare). Most cats (~95%) in the UK are type A. The prevalence of feline blood types varies with breed but type B seems to be seen in higher prevalence (upto 50%) in breeds such as British Shorthair, Birman, Devon Rex and Persian, whilst the majority of domestic shorthair/longhair and Siamese cats tend to be type A (Figure 1). Unlike dogs, cats tend to develop antibodies directed against the opposite blood type antigens A or B. These antibodies can cause destruction of transfused erythrocytes of the opposite blood type. Typically type B cats develop anti-A antibodies earlier than type A cats develop anti-B antibodies but all cats should be assumed to possess alloantibodies. ■■ Most type B cats have high titres of anti-A antibodies and should a type B cat receive type A blood a potentially fatal transfusion reaction can occur. TYpe A TYpe B Figure 1: An increased proportion, but not all, of the individuals of the illustrated breeds will be of the blood type shown here ■■ Type A cats will generally have a lower titre of anti-B antibodies and so should a type A cat receive type B blood, although accelerated destruction may occur, a transfusion reaction is unlikely to be as severe as the other way around. ■■ Type AB cats have neither alloantibody and should ideally receive AB blood, although obtaining an AB
donor can be difficult. Practically type A donor blood would be an appropriate choice for AB cats as it contains low levels of anti-B antibodies to react with the recipient’s AB erythrocytes. As is clearly apparent from this discussion, administering compatible type-specific blood is mandatory in feline transfusion. See Table 1. DOnOR BLOOD GROUp RecipienT BLOOD GROUp A B AB A OK <strong>May</strong>be fatal Possible reaction B Reaction OK Reaction AB Reaction <strong>May</strong>be fatal OK Table 1: Reactions produced between donor and recipient blood types Mik antigen Recently a blood group antigen, and clinically relevant alloantibody, distinct from the AB blood group system has been discovered. Researchers have named this Mik. The absence of Mik can be associated with naturally occurring anti-Mik alloantibodies. In light of this knowledge, and given that more blood group antigens are likely to become known in the future, it is clear that the AB blood group system is simplistic. Therefore, ideally all cats should be cross-matched prior to transfusion, particularly if multiple transfusions are likely. Cross-matching Cross-matching is the gold standard laboratory test used to determine the serological compatibility between the donor and recipient red blood cells and is recommended in all cases. Practically however, cross-matching can not always be performed and its use is typically restricted to animals likely to receive more than one transfusion or before a second transfusion. From a pragmatic point of view, use of typed rather than cross-matched blood is likely to be suitable in most general practice situations. A brief guide to cross-matching, from a previous How to article (companion April 2011) is reproduced in Box 1. BOX 1: ABBreviAted slide crOss‑mAtch pROceDURe 1. Collect blood into an EDTA tube from recipient and donor. 2. Centrifuge tubes to settle the RBCs, remove the supernatant and transfer to a clean, labelled glass or plastic tube. 3. For each donor prepare 3 slides labelled as major, minor and recipient control. 4. Place 1 drop of RBCs and 2 drops of plasma on to each slide according to the following: ■■ Major cross-match = donor RBCs + recipient plasma ■■ Minor cross-match = recipient RBCs + donor plasma ■■ Recipient control = recipient RBCs + recipient plasma 5. Gently rock the slides to mix the plasma and red cells and examine for haemagglutination after 1–5 minutes (presence of agglutination indicates incompatibility); recipient control agglutination will invalidate results. Despite using type-specific blood and performing a cross-match, it is still possible for transfusion reactions to occur, even when donor and recipient appear compatible, and close monitoring is vital during any transfusion. Similarly, warning clients of the possibility of transfusion reactions inspite of compatibility testing, is mandatory before any feline transfusion. Feline blood typing The principle of all veterinary blood typing methods is a visible haemagglutination reaction between patient RBC surface antigens and known reagent monoclonal or polyclonal antisera. There are several different typing kits available. Feline donors and recipients must always be blood-typed due to the naturally occurring antibodies and this can be achieved using simple in-house test kits (for example Alvedia Quick Test A+B) which will type for A, B and AB blood types (Figure 2). It is worth noting that profound autoagglutination, as might be seen with IMHA, will prevent blood typing by in-house methods. Furthermore when an AB result is received it should be checked by an external laboratory for confirmation. companion | 17
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