Platelet Count within the Normal Range at Hospital Admission is Associated with Mortality in Patients with Community-Acquired Pneumonia

Background: Apart from their hemostatic role, platelets are immune cells that play a role in fighting infections. The presence of thrombocytopenia and thrombocytosis at hospital admission are predictors of mortality in community-acquired pneumonia patients. We hypothesized that variations in platelet counts within the normal range also may be associated with mortality in these patients. Methods: The study included all adults in the North and Central Denmark Regions with a first acute hospital admission for community-acquired pneumonia during 2006-2012. We assessed the association between the first platelet count within +/- 24 hours of admission (within the normal range of 150 to 400 x 10(9)/L) and 30-day mortality using Cox models. Analyses were adjusted for age, sex, Charlson Comorbidity Index score, hemoglobin level, leukocyte count, and creatinine level at admission. Results: Among the 12,905 study patients, 30-day mortality was 12.4%. The mean platelet count upon admission was 250 x 10(9)/L. Compared with the 250-275 x 10(9)/L category, platelet counts of 151-175 were associated with a lower 30-day mortality (adjusted hazard ratio [aHR]: 0.79, 95% confidence interval [CI]: 0.63-0.99), while higher platelet counts were associated with a higher 30-day mortality (351-375 x 10(9)/L, aHR: 1.34, 95% CI: 1.07-1.68; 376-400x 10(9)/L, aHR: 1.21, 95% CI: 0.94-1.56). Conclusion: Platelet counts, even within the normal range, are associated with mortality in adult patients hospitalized for community-acquired pneumonia.