Plasma ADAMTS13 activity in dogs with severe thrombocytopenia and presumed immune thrombocytopenia

Abstract

Background: In humans, deficiency of plasma ADAMTS-13, a von Willebrand factor cleaving enzyme, is an important cause of thrombocytopenia in immune thrombotic thrombocytopenic purpura (iTTP). This disease can be difficult to differentiate from immune thrombocytopenia (ITP) in people. Further evaluation of other disease entities such as iTTP-like disease is warranted in subsets of dogs with ITP due to the variability in bleeding tendencies without correlation to platelet counts and poor response to treatment. Hypotheses: Dogs with severe thrombocytopenia and presumed ITP have reduced plasma ADAMTS-13 activity compared to healthy dogs. Additionally, bleeding assessment scores, such as the DOGiBAT, negatively correlate with plasma ADAMTS-13 activity. Animals: Fifteen privately-owned dogs with severe thrombocytopenia and presumed ITP and 40 healthy control dogs enrolled in a separate study recruited from a hospital population. Methods: Prospective observational study. Dogs (≥ 1 year of age) with severe thrombocytopenia (≤20,000 platelets/uL) underwent diagnostic evaluation and were categorized as having presumed primary ITP (pITP) or potential secondary ITP (sITP). All dogs received a DOGiBAT score. Plasma ADAMTS-13 activity was assessed using the Diapharma® RUO Technozyme® ADAMTS-13 Activity ELISA kit. Wilcoxon rank sum test was used to determine if plasma ADAMTS-13 activity is significantly different in dogs with ITP compared to healthy controls. Spearman's rank correlation rho test was used to determine if plasma ADAMTS-13 activity correlates with DOGiBAT scores. Results: Dogs with severe thrombocytopenia and presumed ITP, the combination of presumed pITP and potential sITP, have reduced plasma ADAMTS-13 activity compared to healthy controls (P = 0.039). Individually, plasma ADAMTS-13 activity in dogs with presumed pITP or potential sITP is not different from healthy controls (P = 0.428, P = 0.095, respectively). Plasma ADAMTS-13 activity does not correlate with DOGiBAT scores (P = 0.069). Conclusions and clinical relevance: ADAMTS-13 deficiency may be a mechanism for thrombocytopenia in some dogs with severe thrombocytopenia presumptively diagnosed with ITP.