The impact of platelet count on mortality in unstable angina/non-ST-segment elevation myocardial infarction

Background Expanding the knowledge of pathogenesis of arteriosclerosis points at a central role of platelets in the development of acute coronary syndromes. Therefore, we sought to determine the impact of platelet count on long-term outcome in unstable angina/non-ST-segment elevation myocardial infarction (UA/NSTEMI) receiving contemporary treatment. Methods This prospective cohort study included 1616 consecutive patients with UA/NSTEMI. All patients underwent coronary angiography and, if appropriate, subsequent catheter-based revascularization within 24 hours of admission. Patients were divided in quintiles according to platelet count. The primary end point was all-cause mortality during long-term follow-up of up to 60 months. Results During follow-up (median 17 months, interquartile range 6-31 months), 89 deaths and 74 nonfatal myocardial infarctions occurred. Patients with higher platelet counts were younger, more often female, and had lower height and weight as compared with patients with lower platelet counts. Mortality was significantly lower among patients in the second quintile of platelet count (181-210 x 10(9)/L) as compared with the other quintiles (hazard ratio 0.39, 95% Cl 0.19 to 0.81, P =.011). Kaplan-Meier survival analysis showed cumulative 4-year mortality rates of 12.5%, 3.8%, 10.4%, 9.8%, and 11.4% for patients in the first, second, third, fourth, and fifth quintiles. This association persisted after multivariate adjustment. No association of platelet count and nonfatal myocardial infarctions was observed. Conclusions We found a nonlinear association between platelet count and long-term mortality. The lowest mortality was observed in patients with a platelet count between 181 and 210 x 10(9)/L.