Reduced platelet activity is more common than reported anti-platelet medication use in patients with intracerebral hemorrhage

Background: Anti-platelet medication and reduced platelet activity are associated with an increased risk of death after intracerebral hemorrhage (ICH). The optimal assay for assessing platelet activity is not defined. We hypothesized that reduced platelet activity would be common after ICH. Patients and Methods: We prospectively enrolled 72 consecutive patients with ICH and routinely measured platelet activity with both the PFA-100 (Siemens AG, Germany) and the VerifyNow-ASA (Accumetrics, CA, USA) systems on admission. We prospectively recorded anti-platelet medication use prior to ICH. Results: VerifyNow-ASA measurements were associated with aspirin (P = 0.001) and clopidogrel (P = 0.01) use prior to ICH. Combined clopidogrel and aspirin therapy was more potent than either alone. Of 33 patients with reduced platelet activity on the VerifyNow-ASA assay, 14 (42%) were not known to take anti-platelet agents. Of 27 patients with reduced platelet activity on the PFA-100, a related but different 14 (52%) were not known to take anti-platelet agents. There was a poor agreement between the assays (κ = 0.26, P = 0.07) on which patients had reduced platelet activity among the patients not known to take aspirin. Conclusions: A medication history does not reliably identify patients with reduced platelet activity after ICH, and this may explain studies that found no association between known aspirin use and outcomes. Future studies should screen for unknown use of anti-platelet medications after ICH. Neither assay perfectly identified patients who reportedly used anti-platelet medication before ICH.