Companion May 2012 - BSAVA

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 Maybe fatal Possible
reaction
B Reaction OK Reaction
AB Reaction Maybe 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.
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