Evaluation of Three Whole Blood Platelet Function Tests in Healthy Cats and Effects of Acetylsalicylic Acid and Clopidogrel

Abstract

Feline arterial thromboembolism (ATE) is a well-known complication of hypertrophic cardiomyopathy (HCM). Prophylactic anti-platelet medications, aspirin (ASA) and clopidogrel (CP), are often prescribed in cases of HCM to prevent the occurrence of ATE, however, both occurrence and recurrence occur in spite of therapy. This study evaluated the use of the three point-of-care (POC) platelet function test systems, Multiplate analyzer (MP), Platelet Function Analyzer-100 (PF), and Plateletworks (PW), in healthy cats by developing institutional reference intervals for each test and platelet agonist used. This study also validated the use of PW on flow cytometry-based platelet counts. Using these POC tests, the effect of ASA and CP at standard doses, (ASA 5mg PO Q72h, ASA 20.25mg PO Q72h, and CP 18.75mg PO Q24h), were evaluated. Furthermore, the plasma metabolites of ASA (salicylate) and CP (inactive carboxylic acid derivative SR 26334) were measured to determine if it they correlated with the degree of platelet inhibition measured by the POC tests. MP, PF, and PW institutional references intervals were generated. PW using flow cytometry- based platelet counts correlated with Coulter-based methods. MP had limited utility in detecting any decrease in platelet function irrespective of the treatment administered or platelet agonist used. In contrast, PF and PW had similar results such that, CP when administered alone or in combination with ASA resulted in a measurable decrease in platelet function in response to most platelet agonists. Evaluation of plasma salicylate levels, predicted PF results and moderately correlated with, and weakly predicted, platelet function as measured with PW. Plasma SR 26334 levels, were inconsistently found to be correlated with platelet function measured with MP or PW when using adenosine diphosphate (ADP) agonist. This study also aimed to assess platelet function in cats with HCM at time of diagnosis and after antiplatelet therapy. The desired sample size (n=22) was not recruited, but preliminary results in seven cats were consistent with findings in healthy cats: platelet function at diagnosis was within reference intervals, ASA had minimal effect, and CP effect was noted with PF and PW.