Associations of Thrombocytopenia and Subthreshold Platelet Counts with Clinical Outcomes in Intensive Care Patients: A Prospective Cohort Study

Abstract

Background/Objectives: Thrombocytopenia (TP) is common in critically ill patients, but the significance of its severity, timing, persistence, and admission subthreshold platelet count (PC) remains uncertain. We evaluated these associations with mortality in a medical ICU. Methods: In this prospective cohort study, 280 adults admitted to a tertiary medical ICU (September 2023–August 2024) were followed until ICU discharge or death. TP was defined as a PC < 150 × 109/L, and admission STP as a first ICU PC of 150–199 × 109/L, irrespective of later platelet course. Outcomes included mortality (ICU, hospital, 28-day, 90-day), organ support, and major complications. Results: TP occurred in 118 patients (42.1%), with higher crude mortality at all time points (all p < 0.001). In the lagged time-dependent Cox analysis, ICU-acquired TP was associated with ICU mortality in the minimally adjusted model (HR 1.93, CI 1.12–3.35; p = 0.018) but not after adjustment for invasive MV (aHR 1.31, CI 0.72–2.40; p = 0.372). Admission TP was not significantly associated with ICU mortality in the adjusted model (aHR 1.22, CI 0.74–2.00; p = 0.436). Admission PC showed limited discrimination (AUC 0.583, CI 0.508–0.657). No statistically significant difference was found between admission STP and PC ≥ 200 × 109/L (exploratory comparison, wide CIs). Conclusions: TP was associated with disease severity and worse crude outcomes, but adjusted longitudinal analyses did not establish an independent association with ICU mortality. No statistically significant difference was found for admission STP versus PC ≥ 200 × 109/L in this exploratory comparison; this should not be interpreted as clinical equivalence or as indicating no prognostic value.