Vetnews | Augustus 2024 12 « BACK TO CONTENTS Together, these findings suggest that while blood group systems play an important role in allo geneic blood transfusions within species, they likely hold little predictive or clinical use in xenotransfusion across species. Traditional tube crossmatch methodology typically requires up to 2 mL of EDTA-anticoagulated whole blood, which may be difficult, if not impossible, in small zoological companion animals.24 Safe phlebotomy in zoological companion animals is typically limited to 1% of their respective total body weight, which may often be <1 mL. Consequently, simplified major and minor crossmatches have been employed using a slide agglutination test in which drops of the recipient and donor serum, plasma, or whole blood are mixed on a glass slide at room temperature and examined under a microscope.24 A previous study compared simplified major and minor crossmatches with standard tube crossmatch methodology in rabbits and found close agreement.9 While simplified major and minor crossmatches predict potential agglutination, they cannot predict hemolysis or account for the role temperature plays in alloantibody–alloantigen reactions.24 Hemolysis is considered more clinically significant than agglutination, given that it is suggestive of in vivo intravascular hemolysis, which can result in a systemic inflammatory response, hemodynamic instability, multiple organ dysfunction, and death.8 The alloantibody– alloantigen reactions believed to be most clinically significant in vivo occur at body temperature (warm agglutinins) rather than at room temperature (cold agglutinins).8,9 While the clinical significance of warm and cold agglutinins is not known in rabbits, this study found no significant difference in agglutination pre- and post-incubation across all crossmatches. Although it does not predict hemolysis, simplified crossmatches using a slide agglutination test at room temperature may be a reliable pretransfusion method in rabbits to assess agglutination. Pretransfusion testing in human medicine is highly regulated by governmental and professional healthcare organizations (eg, Federal Drug Administration, American Association of Blood Banks); however, similar stringency and standardization do not currently exist in veterinary medicine.5 As a result, subtle differences exist in major and minor tube crossmatch procedures and interpretation between veterinary emergency and critical care medicine references and referral centers. While the clinical significance of these in vivo differences is unknown, they pose a more immediate potential limitation in comparing and synthesizing in vitro transfusion medicine research. In human transfusion medicine, gel column technology has quickly replaced tube crossmatch methodology due to its many advantages, including speed, standardization, smaller sample volume, and enhanced sensitivity and specificity.25 Although tube crossmatches may be more affordable and accessible to veterinary researchers, gel column crossmatching in veterinary medicine is growing,6,8 and its application to xeno-transfusion across species should be investigated in the future. While this study focused on the 4 major canine and feline blood types historically and most frequently available at referral and veterinary specialty centers, other DEA antigens, the canine Dal antigen, the canine antigens Kai 1 and Kai 2, and the feline Mik antigen could be confounding factors.5,8 Different canine and feline blood-typing methodologies and assays have varying sensitivity and specificity, which could have falsely identified the canine and feline blood donors used in this study. Rabbit recipients only underwent a major crossmatch with 1 randomly assigned rabbit donor due to the finite plasma available. A larger sample size of rabbit recipients and a greater number of crossmatches could have strengthened this study’s findings. The healthy New Zealand White rabbits used in this study were a relatively homogeneous study population in terms of rabbit breed, strain, age, and environmental conditions, which may be different than the heterogeneous population of pet rabbits presented in need of critical care. Although crossmatches were performed and interpreted within 2–4 hours of rabbit blood collection, performing them immediately after phlebotomy could have minimized any potential artifact due to delayed processing. While an autotransfusion or allogeneic blood transfusion is preferred, an emergency xeno-transfusion may provide crucial time for a compatible conspecific donor to be found, a diagnosis to be made, or a patient to respond to therapeutic intervention. This study supports allogeneic blood transfusions between rabbits being highly compatible and builds on the current understanding that rabbits have in vitro serological incompatibility to canine and feline RBCs. This study also suggests rabbits have less in vitro serological incompatibility to feline RBCs if an emergency xeno-transfusion is truly needed. The in vivo serological compatibility and subsequent risk of transfusion reactions in rabbits receiving xeno--transfusions with canine or feline blood products remain unclear. Clinicians should continue to carefully weigh pretransfusion testing with the therapeutic needs of a severely anemic rabbit. A major crossmatch (via tube or simplified methodology) is recommended prior to xenotransfusion to a rabbit recipient, knowing that donor RBC survival will likely be decreased, and the degree of any in vitro crossmatch incompatibility may not be predictive of in vivo serological compatibility. ACKNOWLEDGMENTS The authors thank Andrea Thompson, Alexis Sluder, Coralie Zegre Cannon, and Alicia Ossi for their assistance in sample collection, as well as Lynnette McCall, Charlotte Shaughnessy, and the North Carolina State University College of Veterinary Medicine Clinical Pathology Laboratory for providing equipment, laboratory space, and crossmatch expertise. The authors also thank the amazing canine and feline blood donors whose generous contributions make the North Carolina State University College of Veterinary Medicine Blood Bank possible. v CONFLICT OF INTEREST STATEMENT The authors declare no conflicts of interest. ORCID Nicholas G. DannemillerDVM https://orcid.org/0000-0003-3429- 1881 SarahM.OzawaDVM,DACZM https://orcid.org/0000-0002-9038- 8795 Sarah E.MusulinDVM,DACVECC https://orcid.org/0000-0002- 5420-0601 ENDNOTES aKetaset Zoetis Inc., Kalamazoo, MI. bXylaMed MWI Animal Health, Boise, ID. c QuickTest A+B Alvedia, Limonest, France. d Animal Blood Resources International, Stockbridge,MI. e https://pairs. austincodingacademy.com/ fR Core Team, Vienna, Austria. Leading Article References available on request.
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