Introduction: In feline blood transfusion, life-threatening immune-mediated hemolytic reactions can appear because of red blood cells (RBCs) agglutination due to naturally occurring alloantibodies against erythrocytes antigen. The most described erythrocyte antigens system in cats is the AB system. Crossmatch (XM) tests are mandatory to prevent incompatible transfusion if typing is not available and could be recommended in addition of blood typing to detect severe non-AB incompatibility.

Background: Gold standard XM tests as well as reliable bedside tests are lacking in cats.

Objective: To compare strength of agglutination between six crossmatch test methods described in feline transfusion medicine.

Methods: Plasma from a type B cat, plasma from a type A cat and RBCs from a type A cat where used to perform crossmatch tests. RBCs solution was diluted to obtain a scale of agglutination reactions. Using each dilution of RBCs, XM tests were performed using six XM methods: gel column card without antiglobulin, gel with antiglobulin, immunochromatographic strip, tube, rapid slide and microscope.

Results: The gel column card XM test showed strong agglutination until the dilution 1/80 and became negative at 1/110. The XM gel with antiglobulin showed strong agglutination up to the dilution 1/64 and became negative at 1/100. The immunochromatographic strip XM demonstrated strong agglutination until the dilution 1/50 and became negative at 1/64. Large agglutinates were observed until the dilution 1/64 on tube method. Large agglutinates were observed until the dilution 1/50 on rapid-slide and microscope methods and no microagglutination was seen after the dilution 1/100.

Discussion: Gel XM methods can detect smaller agglutination reactions but could also detect any agglutination due to an underlying disease process; they are time-consuming and require experienced operator. All currently available XM methods are able to detect strong agglutination reactions, which are the ones that lead to most severe hemolytic reactions. To date, clinical relevance due to weak agglutination reactions is unclear.

Conclusion: XM techniques with gel are more sensitive to detect weak agglutination reactions in cats compared to other techniques. All techniques are able to detect strong agglutination reactions and exclude risk of severe AB (and non-AB) acute reactions.