Blood transfusions are a life-saving tool in feline medicine, used to treat anemias caused by trauma or internal blood loss, red cell destruction due to infection or autoimmune disease, surgical bleeding, renal failure, or a multitude of other causes. For severely anemic animals, the availability of blood makes the difference between life and death. The demand for feline blood has traditionally been much less than that of canine, and the short shelf-life of stored blood makes banking impractical for many smaller institutions. Transfusion of freshly collected blood is often utilized, however this relies on the availability of a matched donor cat. Type “A” cats are by far the most common, however “B” cats are much more scarce. Donor cats must also be an adequate size, be negative for any infectious disease, and be healthy enough to donate blood.
While xenotransfusion (the administration of blood from one species to another) has fallen out of favour in human and canine medicine, it is still sometimes used with reported success in feline practice. The administration of dog blood to anemic cats has been shown many times to be well tolerated for a single transfusion (additional transfusions are usually fatal due to the development of strong antibodies). While canine blood does not last long in a cat, it can be enough to save a life in an emergency situation, and is much more readily available than feline blood, especially for type B cats (as transfusion of A blood to B cats is immediately fatal).
Cross-matching is a technique whereby blood of different individuals is mixed together in specific laboratory conditions to evaluate the potential for transfusion reactions. A major cross match evaluates donor cells against recipient plasma, and a minor evaluates recipient plasma against donor cells. A positive match generally indicates that transfusion should not be performed (especially for a major cross match).
The purpose of this study was to determine if cats and dogs produce naturally occurring antibodies to each other’s blood (ie without a previous transfusion).
Surplus blood from 34 cats and 42 dogs admitted to the veterinary hospital at the University of Messina were included in the study. Dogs were blood typed for DEA 1.1 with a commercial kit, and cats for A/B/AB with a tube agglutination method. 15 dogs were DEA 1.1 negative and 27 DEA 1.1 positive. 27 cats were type A, 3 type B, and 4 type AB (an unusually large amount for most areas of the world).
After typing, blood from each cat was cross matched with blood from between 2 to 6 dogs for a total of 111 cross matches. 97 of these were full cross matches (major and minor, at 4 degrees, room temperature, and 37 degrees).
Of the major cross matches, 74% were positive at 37 degrees, 82% at room temperature, and 86.5% at 4 degrees. Minor cross matches were positive in 98.1% of cats at 37 degrees, 0% at room temperature, and 99% at 4 degrees. No cat tested fully negative against any dog. Only 25.2% of cats were negative for a major cross match at body temperature (the most clinically relevant component of the test).
This study provides significant evidence that there are naturally occurring incompatibilities between feline and canine blood on both major and minor cross match in the majority of animals. This suggests that transfusion reactions should be encountered with a large number of canine to feline xeontransfusions - a result which conflicts with previous in vivo studies and many practitioner’s anecdotal experience. The authors suggest several possible reasons for this, including unobserved or unreported reactions, differences in antibodies by geography or time, or a lack or correlation between cross matching and clinical signs. Regardless of the cause, further data should be collected on the association between positive cross matches and transfusion reactions in cats.
A further drawback to the study was the fairly low numbers of type B and AB cats. Further work with larger numbers of these less common blood types should be performed, including analysis of other factors such as the Mik antigen.
An interesting discovery in this study was that while all cats had high rates of positive cross matches, Type B cats with DEA 1.1 negative dogs had the lowest rate of reactions. This is beneficial, as it is potentially the most likely situation to occur in practice.
Transfusion of canine blood to cats is not recommended. However, in emergent situations it may be necessary. The authors recommend that in this case, cross-matching should be performed and an attempt made to find a donor who - at the very least - tests negative on a major cross match at 37 degrees.
