Platelets and mortality in bloodstream infection: a multicenter cohort study.

Objective: The objective of this study was to determine whether thrombocytopenia is independently associated with mortality in patients with bloodstream infections (BSIs) and compare the impact of platelets on mortality with that of white blood cells and neutrophils.

Methods: This retrospective cohort study used the following two U.S. cohorts of patients with BSIs: (1) patients at a multihospital network in the metropolitan Houston, Texas, area between July 01, 2016 and June 17, 2023, and (2) patients in the publicly available Medical Information Mart for Intensive Care (MIMIC)-IV database (2008-2022). We included patients who had their platelets checked in the 48 hours before positive blood culture collection. We created multivariable logistic regression models to determine whether 30-day in-hospital mortality was impacted by the degree of thrombocytopenia (severe [platelets <50 k/μL], moderate [50-99 k/μL], mild [100-149 k/μL], and none [≥150 k/μL]).

Results: We included 21105 patients in the Houston cohort and 2710 in the MIMIC-IV cohort, and 30-day mortality in the Houston cohort was 12.0% (2524/21105) and was significantly associated with the platelet count. After controlling for confounders, the adjusted odds ratio (aOR) for 30-day mortality with severe thrombocytopenia was 4.66 (95% CI, 3.91-5.55); aOR for moderate thrombocytopenia was 2.61 (95% CI, 2.25-3.02); and aOR for mild thrombocytopenia was 1.55 (95% CI, 1.37-1.76), all compared with normal platelet counts (≥150 k/μL). The adjusted odds of death with severe thrombocytopenia were greater than those with neutropenia, leukopenia, or leukocytosis. Results were similar in multiple sensitivity analyses and in the MIMIC-IV cohort.

Discussion: Thrombocytopenia was independently associated with mortality among patients with BSIs. Platelet counts can provide clinicians a readily available way to risk-stratify patients with BSI, and future research should examine the mechanisms by which platelets are protective in BSI.