Do point-of-care platelet function tests agree with conventional light transmission aggregometry in identifying aspirin nonresponsiveness in patients after TIA or ischemic stroke?
Different platelet function tests yield highly discordant rates of aspirin nonresponsiveness, highlighting the need for standardized, prognostically validated testing methods.
BACKGROUND AND PURPOSE: Recent studies suggest that patients who do not respond to aspirin (ASA) therapy may be at increased risk of ischemic vascular events. The availability of simple to use point-of-care (POC) platelet function tests now potentially allows aspirin nonresponsiveness to be identified in routine clinical practice. However, there are very few data on whether the different tests produce consistent results. We therefore compared 2 POC tests (PFA-100 device and the Ultegra-RPFA RPFA) with conventional light transmission aggregometry (LTA). METHODS: Platelet function was assessed by all 3 tests in 100 patients receiving low-dose ASA therapy after transient ischemic attack (TIA) or ischemic stroke. RESULTS: The incidence of ASA nonresponsiveness was 17% by the RPFA and 22% by the PFA-100, compared with only 5% by LTA (ie, as defined with both arachidonic acid and ADP). Agreement between the RPFA and the PFA-100 and arachidonic acid induced LTA was poor (kappa=0.16, 95% CI, -0.08 to 0.39, P=0.11; and kappa=0.09 -0.12 to 0.30, P=0.32, respectively). Agreement between the 2 POC tests was also poor (kappa=0.14, -0.08 to 0.36, P=0.15). Only 2% of patients were aspirin nonresponders by all 3 tests. CONCLUSIONS: The prevalence of apparent ASA nonresponsiveness was higher with both the POC tests than with LTA. However, agreement between the tests was poor and very few patients were ASA nonresponsive by all 3 tests. Aspirin nonresponsiveness is therefore highly test-specific and large prospective studies will be required to determine the prognostic value of each of the separate tests.
Harrison et al. (2005) studied this question.