Published Online
on April 7, 2005

A more recent version of this article appeared on May 1, 2005

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Submitted on January 8, 2005
Accepted on January 21, 2005

Screening for Aspirin Responsiveness After Transient Ischemic Attack and Stroke. Comparison of 2 Point-of-Care Platelet Function Tests With Optical Aggregometry

Paul Harrison PhD; Helen Segal PhD; Kevin Blasbery BSc; Charlene Furtado BSc; Louise Silver MSc; and Peter M. Rothwell PhD, FRCP^*

From the Oxford Haemophilia Centre & Thrombosis Unit (P.H., K.B., C.F.), Churchill Hospital, Oxford, UK; and the Stroke Prevention Research Unit (H.S., L.S., P.R.), Department of Clinical Neurology, University of Oxford, UK.

^* To whom correspondence should be addressed. E-mail: peter.rothwell{at}clneuro.ox.ac.uk.

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 (=0.16, 95% CI, -0.08 to 0.39, P=0.11; and =0.09 -0.12 to 0.30, P=0.32, respectively). Agreement between the 2 POC tests was also poor (=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.

Key words: aspirin • platelets

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