Procoagulant Microparticles in Dogs with Immune-Mediated Hemolytic Anemia.

Background Studies of some human prothrombotic diseases suggest that phosphatidylserine-positive ( PS+) and tissue factor-positive ( TF+) microparticles ( MPs) might play a role in the pathogenesis of thrombosis or serve as biomarkers of thrombotic risk. Hypothesis/Objectives To determine if circulating levels of PS+ MP and procoagulant activity ( PCA) associated with PS+ MPs and TF+ MPs are increased in dogs with IMHA. Animals Fifteen dogs with primary or secondary IMHA and 17 clinically healthy dogs. Methods Prospective case-controlled observational study. Circulating PS+ MPs were measured by flow cytometry. PCA associated with PS+ MPs and TF+ MPs was measured by thrombin and Factor Xa generating assays, respectively. Results Circulating numbers of PS+ MPs were not significantly higher in dogs with IMHA [control median 251,000/μL (36,992-1,141,250/μL); IMHA median 361,990/μL (21,766-47,650,600/μL) P = .30]. However, PS+ MP PCA [control median 2.2 (0.0-16.8) nM PS eq; IMHA median 8.596, (0-49.33 nM PS eq) P = .01] and TF+ MP PCA [control median 0.0, (0.0-0.0 pg/mL); IMHA median 0.0; (0-22.34 pg/mL], P = .04) were increased. Intravascular hemolysis, which we showed might increase PS+ and TF+ MP PCA, was evident in 3 of 5 dogs with PS+ MP PCA and 2 of 4 dogs with TF+ MP PCA higher than controls. Underlying disease in addition to IMHA was detected in 1 of 5 dogs with PS+ PCA and 3 of 4 dogs with TF+ MP PCA higher than controls. Conclusions and Clinical Importance TF+ and PS+ MP PCA is increased in some dogs with IMHA. Further studies that determine if measuring TF+ and PS+ MP PCA can help identify dogs at risk for thrombosis are warranted. [ABSTRACT FROM AUTHOR]