Detection and dynamics of anti‐platelet antibodies in thrombocytopenic dogs with and without idiopathic immune thrombocytopenia

Abstract

Background Antiplatelet antibodies are detected in multiple diseases including primary immune thrombocytopenia (ITP). Dynamics of how these antibodies change over time in ITP is unknown in dogs. Hypothesis/Objectives Antiplatelet antibodies (APA) will be detected in thrombocytopenic dogs with multiple etiologies and dynamics of APA in dogs with ITP can be used to evaluate response to treatment and relapse. Determine APA at the time of diagnosis in thrombocytopenic dogs and serially in primary ITP dogs. Animals Seventy‐nine thrombocytopenic dogs and 28 primary ITP dogs. Methods Direct flow cytometry was performed in thrombocytopenic dogs at initial evaluation and serially in suspected primary ITP dogs. In primary ITP dogs, a 2‐tailed Fisher's exact test was performed comparing survival to discharge between dogs with and without melena and to relate response to treatment and relapse to changes in APA and platelet count (repeated measures analysis, Spearman correlation). Results Twenty percent (16/79) of thrombocytopenic non‐ITP dogs with infectious, neoplastic, or other diseases and all primary ITP dogs were positive for APA. Melena at initial evaluation was associated with decreased survival to discharge (odds ratio 0.06; P = .01). Persistence of APA was not associated with response to treatment, but recurrence of antibodies was associated with relapse (odds ratio 205.0; P < .01). There was no difference in percentage of APA or platelet count at initial diagnosis between dogs that did or did not respond to treatment. Conclusions and Clinical Importance Serial monitoring of APA in dogs with primary ITP appeared beneficial for determining relapse of disease.

Preliminary evaluation of a flow cytometric assay with microsphere controls for the detection of platelet‐bound antibodies in canine immune thrombocytopenia

“…Moreover, many different criteria have been used to define a “positive” result. Stated positive PSAIg criteria have included absolute shifts in fluorescence intensity of bound label to greater than 10 MFI, 27 MFI values greater than 2 SD above that of healthy dog platelets, 23 comparisons of labeling with same‐day samples from healthy dogs, 4 and an increment in fluorescence beyond that of an isotype label 4,7 . Reported sample stability for PSAIg assays also vary widely, ranging from 3 hours 2 to 3 days 7,27 .…”

“…Stated positive PSAIg criteria have included absolute shifts in fluorescence intensity of bound label to greater than 10 MFI, 27 MFI values greater than 2 SD above that of healthy dog platelets, 23 comparisons of labeling with same‐day samples from healthy dogs, 4 and an increment in fluorescence beyond that of an isotype label 4,7 . Reported sample stability for PSAIg assays also vary widely, ranging from 3 hours 2 to 3 days 7,27 . Not surprisingly, combined preanalytic and analytic variability and an inconsistent definition of a positive PSAIg test, have resulted in a broad range of expected positive PSAIg values (from 1% to 24%) for healthy dogs.…”

“…Thrombocytopenia is a common hemostatic defect, and immune‐mediated platelet destruction is a frequent cause of severe thrombocytopenia in dogs 1–3 . Various disease conditions are associated with secondary immune thrombocytopenia (ITP), including infectious agents, drug therapies, lymphoproliferative disease, and other neoplastic disorders 1,2,4–8 . In contrast, primary or autoimmune thrombocytopenia is characterized by isolated thrombocytopenia in the absence of an underlying disease process or abnormalities in other cell lines 3,9 .…”

“…The human disease counterpart of canine primary ITP is referred to as adult chronic ITP 10,11 . In both species, autoantibodies targeting platelet antigens led to pathologic platelet clearance 3,7,10,12 . Detailed immunologic studies in people have revealed that T cell‐mediated cytotoxicity and T‐regulatory cell imbalance also contribute to platelet destruction 10,13,14 .…”

“…Although antiplatelet antibodies are implicated in the pathogenesis of thrombocytopenia, the detection of these antibodies is not included in diagnostic guidelines for chronic ITP 11,15 . However, recent studies suggest that individual patient monitoring to detect changes over time in platelet autoantibodies could aid in predicting treatment responses and relapse 7,16,17 . While the presence of antiplatelet antibodies did not predict initial treatment responses in a clinical case series of dogs with primary ITP, recurrence of detectable platelet autoantibodies was associated with a relapse of thrombocytopenia unlike those without detectable platelet antibodies 7 …”