Platelet counts of adults upon acute hospital admission to internal medicine units are a predictor of mortality

The objective of this cohort study was to examine the association between platelet counts upon acute hospitalization and mortality. The study included all adults in North and Central Denmark Regions with a first acute admission to an internal medicine unit during 2006–2012, categorized by first platelet count within +/−24 hours of admission. We assessed the association between platelet count and in-hospital, 30-day, 90-day, and 365-day mortality using age- and sex-adjusted Cox models. We also stratified analyses by presence/absence of comorbidity and performed additional analyses restricted to patients with a primary discharge diagnosis of cardiovascular disease or infection. Among the 274,148 study patients, the 1-year mortality was 12.6%. The association between platelet count and mortality took the form of an asymmetric U-shaped curve. For 30-day mortality, hazard ratios (HRs) were 5.24 (95% CI: 4.60–5.97) for platelet count < 50 × 10⁹/L and 2.50 (95% CI: 2.33–2.69) for platelet count ≥ 500 × 10⁹/L, compared with a normal platelet count (150–400 × 10⁹/L). A slightly increased risk of mortality was observed for platelet counts < 200 × 10⁹/L and ≥ 250 × 10⁹/L. A similar pattern was observed for 30-day, 90-day, and 365-day mortality and in all subgroups except patients with a primary discharge diagnosis of infection. In this case, patients with a platelet count between 150 × 10⁹/L and 199 × 10⁹/L had the lowest mortality. Platelet counts in adults upon acute hospital admission to internal medicine units, including counts within the normal range, are a predictor of mortality.