Objectives: To establish whether heightened platelet activation is a common feature of canine immune-mediated haemolytic anaemia, and to evaluate the hypothesis that platelet activation plays a role in the pathogenesis of thromboembolism.

Methods: Using whole-blood flow-cytometric analysis, the proportion of activated platelets and platelet-leucocyte aggregates in blood samples from 14 dogs with immune-mediated haemolytic anaemia and 14 healthy dogs was calculated. General linear models with binomial errors were used to compare groups. Results from the immune-mediated haemolytic anaemia-affected dogs were then correlated with established risk factors for thromboembolism in canine immune-mediated haemolytic anaemia, D-dimer concentration and antithrombin activity.

Results: There was a strong correlation between platelet activation and severe thrombocytopenia, with heightened platelet activation being observed predominantly in severely thrombocytopenic dogs.

Clinical Significance: Dogs with immune-mediated haemolytic anaemia, particularly those with concurrent severe thrombocytopenia, are likely to have heightened platelet activation, which may play a role in the pathogenesis of thromboembolism.