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 ( MP s) 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 + MP s and TF + MP s 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 + MP s were measured by flow cytometry. PCA associated with PS + MP s and TF + MP s was measured by thrombin and Factor Xa generating assays, respectively. Results Circulating numbers of PS + MP s 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.