Background: Aspirin has a wide interindividual inhibitory effect on platelets potentially resulting in either bleeding or breakthrough thrombosis. Immature circulating platelets are inhibited less by aspirin and can be readily quantified using the immature platelet count (IPC) or immature platelet fraction (IPF) parameters.

Aims:  We investigated whether IPC or IPF were associated with platelet functional responses in patients receiving aspirin monotherapy at the time of cardiac surgery.

Methods: Patients were recruited at the Bristol Heart Institute between March 2010 and August 2012 (ISRCTN 20778544). IPC (the product of platelet count (PLT) and IPF) and Multiplate® platelet functional responses with TRAP-test, ASPI-test and ADP-test reagents and with adrenaline 100mg/ml were measured just prior to surgery. Relationships were explored between inverse normal transformed test results.

Results: Of 1109 patients receiving aspirin, 79.6% were male and the mean age was 68.3 years. 961 (86.7%) patients underwent coronary artery bypass (± valve) surgery. Common comorbidities included diabetes (22.4%), hypertension (76.5%) and previous myocardial infarction (25.6%). The median IPC was 5.43 x10⁹/L (range 1.02-27.5). Compared to patients not taking anti-platelet therapy, the median ASPI-test Multiplate® response (64.1 AU, range 3.8-263.6) was reduced, in keeping with aspirin use. The median ADP-, TRAP-test and adrenaline responses were comparable to non-aspirin takers. In unadjusted linear regression analyses IPC, but not IPF, was positively associated (p <0.0001) with Multiplate® responses to all activating agonists. This association persisted in a least squares multivariable model after adjustment for age, sex, BMI, comorbidities, type of surgery and PLT.

Forest plot of unadjusted and multivariable linear regression analyses for IPC vs Multiplate® responses

Conclusions: IPC is a widely available and readily standardised parameter derived from the full blood count test result. In this largest reported study cohort, the association between IPC and Multiplate® responses suggests that IPC may be a clinically useful way of identifying both low and high responders to aspirin, potentially enabling prediction of adverse thrombotic and bleeding outcomes respectively.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/immature-platelet-count-is-associated-with-platelet-functional-responses-in-patients-receiving-aspirin/