Abstract. The objectives of this study were to establish feline references intervals for 3 commercial whole blood platelet function test analyzer systems: Multiplate analyzer (MP; Roche Diagnostics International Ltd., Rotkreuz, Switzerland), Platelet Function Analyzer-100 (PF: Siemens Canada, Mississauga, Ontario, Canada), and Plateletworks Combo-25 kit (PW; Helena Laboratories, Beaumont, TX). Venipuncture was performed on 55 healthy sedated cats, and platelet aggregation in response to adenosine diphosphate (ADP), collagen (COL), and arachidonic acid (AA; MP only) was assessed using citrated blood. For the MP analyzer, median (95% confidence intervals [CIs]) area under curve (Units) for ADP, COL, and AA agonists were 87 (11-176), 81 (32-129), and 91 (59-129), respectively. For the PF analyzer, median (95% CIs) closure time, using COL-ADP cartridges, was 69 (46-89) sec. For the PW assay, median (95% CIs) percent aggregations for ADP and COL agonists were 71 (18-92) and 49 (9-96), respectively, using impedance hematology analyzer platelet counts, and 94 (25-98) and 68 (14-119), respectively, using flow cytometry hematology analyzer platelet counts. There were low correlations between the PF analyzer (COL-ADP cartridge) and MP analyzer (COL agonist; ρ = 0.11), and between the PF analyzer (COL-ADP cartridge) and PW assay (COL agonist using impedance platelet counts; ρ = 0.14). The PW assay percent aggregations using impedance and flow cytometric platelet counts were correlated for both ADP (ρ = 0.64) and COL (ρ = 0.64) agonists. Platelet function testing using these tests are feasible in cats, but 95% CIs are wide, so single results may be difficult to interpret. Platelet counting by impedance or flow cytometry may be used for the PW assay but are not interchangeable.

Objectives The objective was to determine if decreased platelet function could be detected after treatment with aspirin and/or clopidogrel in healthy cats using three point-of-care platelet function tests that evaluate platelet function by different methods: Multiplate (by impedance), Platelet Function Analyzer 100 (by mechanical aperture closure) and Plateletworks (by platelet counting). Methods Thirty-six healthy cats were randomly assigned to receive one of three oral treatments over an 8 day period: (1) aspirin 5 mg q72h; (2) aspirin 20.25 mg q72h; or (3) clopidogrel 18.75 mg q24h. Cats treated with 5 and 20.25 mg aspirin also received clopidogrel on days 4-8. Platelet aggregation in response to adenosine diphosphate and collagen ± arachidonic acid was assessed on days 1 (baseline), 4 and 8. Aspirin and clopidogrel metabolites were measured by high-performance liquid chromatography. Platelet function in response to treatment was analyzed by ANCOVA, linear regression and Spearman correlation. Results The only solitary aspirin effect was detected using Plateletworks with collagen in cats treated with 20.25 mg. The only effect detected by Multiplate was using arachidonic acid in cats treated with both aspirin 20.25 mg and clopidogrel. All clopidogrel treatment effects were detected by Platelet Function Analyzer 100, Plateletworks (adenosine diphosphate) and Plateletworks (collagen). Drug metabolites were present in all cats, but concentrations were minimally correlated to platelet function test results. Conclusions and relevance Platelet Function Analyzer 100 and Plateletworks using adenosine diphosphate ± collagen agonists may be used to detect decreased platelet function in response to clopidogrel treatment. Either aspirin is not as effective an antiplatelet drug as clopidogrel, or the tests used were not optimal to measure aspirin effect. Cats with heart disease are commonly prescribed antiplatelet drugs to decrease the risk of aortic thromboembolism. Platelet Function Analyzer 100 and Plateletworks may be useful for confirming clopidogrel treatment in these cats.