Is Xenotransfusion of Canine Blood to Cats Really a Bad Practice?

The first blood transfusion in a human was a xenotransfusion (donor and recipient of different species). On June 15, 1667, a French doctor, Jean Baptiste Denis, assisted by surgeon Paul Emmerez, transfused blood from a sheep to a 15-year-old man who had been suffering from a fever for 2 months but subsequently made a full recovery (Denis 1667). The first allotransfusion (both recipient and donor of same species) into a human did not take place until 1818 (Blundell 1818). However, after the death of a patient 2 months following a second xenotransfusion, transfusion was outlawed in France in 1670 and then in other countries (Roux et al. 2007). It was only after 1900, with the discovery of human blood groups by Karl Landsteiner, that transfusion, specifically allotransfusion, flourished. In veterinary medicine, xenotransfusion of dog blood to cats has long been commonly practised because of the risks of anaphylaxis following allotransfusion in the cat. However, the risks and benefits of xenotransfusion in cats are uncommonly reported (Bovens & Gruffydd-Jones 2013) and for 46 years, from 1968 to 2014, there were no publications on xenotransfusion from dogs to cats. Although recent improvement in identification of cat blood type has allowed a resurgence of allotransfusion, xenotransfusion has not died out. A recent survey on transfusion in cats in France reported that 30% veterinarians exclusively used canine blood to transfuse cats, while another 22% used both canine and feline blood; only 48% of the veterinarians questioned used only feline blood (Fert 2018). In this issue of JSAP, Le Gal et al. (2020) report the largest case series of dog-to-cat xenotransfusions, confirming previous observations regarding its relative safety. The authors studied the characteristics and outcome of 49 cats that received xenotransfusion with canine blood in two university referral hospitals between January 2016 and July 2018. Attending clinicians performed xenotransfusion only if feline blood products were unavailable and if they considered the cat likely to die within 6 hours without blood. The median volume transfused was 14.6 mL/kg. Few febrile reactions, which were without sequelae, and no other acute transfusion reactions were observed. In about two thirds of the cats that did not die rapidly of their presenting disease, there was a delayed haemolytic transfusion reaction, manifesting largely as icterus and haemolytic serum after a median of about 2 days, which is earlier than previously reported. Incompatibilities between donors and recipients did not predict the development of a delayed haemolytic transfusion reaction. In this group of extremely sick patients it may difficult to differentiate causes of morbidity and mortality, but all the non-surviving cats in this study were considered to have died of the underlying disease process rather than the xenotransfusion. It should be noted that many surviving cats also received subsequent transfusions of cat blood. The benefits observed, the absence of severe adverse effects, the relative ease of collecting blood from dogs rather than cats and the absence of intra-species infectious risks support the relative safety of xenotransfusion of canine blood to cats and, therefore, its application in emergencies. As the authors note, it is absolutely imperative that owners realise the importance of their cat having had a cross-species transfusion and the necessity of communicating that information to any veterinarian that treats their cat in future! The author declares no conflict of interest.