The prognostic role of platelet count dynamics in patients hospitalized with acute coronary syndromes (ACS) remains unclear. This study investigated the implications of platelet counts and their changes in ACS patients, using MATRIX trial data.

In-hospital relative changes in platelet count were analyzed continuously and were categorized into groups. Associations with 1-year risks of mortality and major or clinically relevant nonmajor bleeding were modelled using Cox regression.

Among 7722 ACS patients, a platelet count drop >10% occurred in 47.5% of the patients and a platelet count increase >10% in 6.4%. Platelet count changes showed a U-shaped association with mortality and an L-shaped association with bleeding. Compared with the reference group (from 10% drop to 10% increase; rates: mortality 2.6%, bleeding 6.2%), platelet count drops were associated with an incremental mortality risk of approximately 30% (30%-50% drop: 9.5%; HR, 2.86; 95%CI, 1.93-4.23]; >50% drop: 21.4% HR, 3.86; 95%CI, 2.21-6.74) and a bleeding risk of approximately 10% (10%-30% drop: 8.2%, HR, 1.34; 95%CI, 1.11-1.61; 30%-50% drop: 13.8%, HR, 2.01; 95%CI, 1.48-2.72; >50% drop: 32.1%; HR, 4.59; 95%CI, 3.01-6.99). Platelet count increases were associated with an incremental mortality risk of approximately 10% (10%-30% increase: 5.8%; HR, 1.87; 95%CI, 1.18-2.98; 30%-50% increase: 8.5%; HR, 2.61; 95%CI, 1.05-6.44; >50% increase: 9.7%; HR, 3.51; 95%CI, 1.10-11.22) but not with bleeding.

In ACS patients, platelet count drops were associated with incremental risks of mortality and bleeding, whereas platelet count increases were associated with an incremental risk of mortality but not bleeding.