Is platelet phospholipid-dependent thrombin generation altered by acute myocardial infarction or aspirin?

The ability of unactivated and calcium ionophore activated platelets to support thrombin generation in defibrinated plasma was measured by a chromogenic substrate assay in the absence of clot formation. Platelet phospholipid-dependent thrombin generation (Platelet-TG) could be measured using platelets isolated from blood collected into either sodium citrate or EDTA as anticoagulant. Measurements were stable in samples kept at room temperature for 24 hours after venesection. There was no significant difference in either the unactivated or activated platelet-TG with platelets collected into either anticoagulant (mean difference 10.12 nmol/min unactivated and 10.60 nmol/min activated). There was no correlation between unactivated and activated platelet-TG and patient age. Platelet-TG was 179 (153-237) nmol/min (median and inter-quartile range) for unactivated and 489 (462-508) nmol/min for activated platelets from healthy volunteer subjects (median age 31, range 20-40 years). Platelet-TG was the same in subjects from a population-based cohort study (median age 58, range 45-70 years [162 (142-193) nmol/min and 527 (490-551) nmol/min, unactivated and activated platelets respectively] as compared to patients admitted with acute myocardial infarction (median age 68, range 36-85 years [179 (146-200) nmol/min and 473 (440-517) nmol/min unactivated and activated platelets respectively] (p=0.497 for comparison between unactivated platelet-TGs and p=0.487 for comparison between activated platelet-TGs in the two groups). Aspirin inhibited platelet aggregation but did not affect platelet-TG using either unactivated or activated platelets exposed to aspirin in vitro; or in vivo, using platelets obtained from individuals after ingestion of aspirin. In conclusion these results show that for measurement of platelet -TG, blood samples can be anticoagulated with EDTA as well as sodium citrate for up to 24 hours after venesection and that this measurement is not affected by subject age, aspirin treatment or the acute stage of myocardial infarction.