Assessment of platelet inhibition secondary to clopidogrel and aspirin therapy in preoperative acute surgical patients measured by Thrombelastography Platelet Mapping.

Background: Increasing numbers of patients prescribed clopidogrel and aspirin are presenting for non-elective surgery. No consensus on the timing of surgery exists after withdrawal of antiplatelet and tests of platelet function are not routinely available. The Thrombelastography Platelet Mapping (TEG-PM) assay is designed to assess platelet inhibition secondary to antiplatelet therapy. We assessed its ability to detect platelet inhibition in preoperative acute surgical patients.

Methods: We conducted a prospective observational study in three groups of preoperative patients: those taking clopidogrel or aspirin up to admission, and a control group. TEG-PM was performed on the day of admission and alternate days until surgery.

Results: Mean (SD) platelet thromboxane A(2) receptor inhibition in the control group was 17.5% (23.8) (n=20), 52.6% (32.3) (n=18) in the aspirin group, and 31.9% (27.6) (n=21) in the clopidogrel group (P<0.01). Mean (SD) platelet adenosine diphosphate (ADP) receptor inhibition in the control group was 47.8% (18.9) (n=20), 52.6% (19.7) (n=18) in the aspirin group, and 71.5% (18.4) (n=21) in the clopidogrel group (P<0.01). Among the clopidogrel group awaiting surgery, mean platelet ADP channel inhibition decreased on day 3 to 67.1% (24.7) (n=11), 48.8% (24.4) (n=4) on day 5, and 36.1% (15.9) (n=2) on day 7 (P=0.57).

Conclusions: TEG-PM can identify statistically significant platelet inhibition after antiplatelet therapy; however, the overlap in platelet receptor inhibition between the three groups is likely to limit the clinical usefulness of this test.