Reactive thrombocytosis in acute infectious diseases: Prevalence, characteristics and timing

Published:February 19, 2019DOI:


      • Thrombocytosis was found in ~8% of 421 patients admitted with acute infections.
      • Thrombocytosis was positively correlated with acute-phase reactants (ESR, CRP).
      • Patients with reactive thrombocytosis had more bacteremias and longer hospital stay.
      • Patients had more suppurative complications/mortality affecting a minority (12.5%).
      • Thrombocytosis was often mild, present on admission, and always transient.



      Reactive thrombocytosis is known to occur in infectious, inflammatory and neoplastic diseases. However, the characteristics of its association with acute infections (ID) has not been systematically studied.


      A department of internal medicine in a general teaching hospital.


      Retrospective chart review of admitted patients with a confirmed diagnosis of community-acquired pneumonia (CAP), urinary tract infection (UTI) or skin and soft tissue infection (SSTI). Key clinical and laboratory data were retrieved and patients with platelet counts >400 × 109/L who had no alternative cause of thrombocytosis were studied longitudinally and compared to patients with acute infections who had no thrombocytosis.


      Thirty two of 421 patients with acute infections (ID) had infection-associated thrombocytosis (7.6%): 11/125 patients with CAP (8.8%), 13/205 patients with UTI (6.3%) and 8/91 (8.8%) patients with SSTI. Their median ages (77–78 years), gender (48% males), admission temperature, Hb, and WBC were not significantly different from ID patients without thrombocytosis. However, patients with thrombocytosis had longer hospital stays (P = 0.001), more bacteremias (P = 0.048) and in 4/32 (12/5% vs. 2%) significantly increased combined mortality or suppurative complications (P = 0.0006). The ESR (median 70 vs. 40 mm/h, P = 0.000) and CRP (median 214 vs. 114 mg/dL, P < 0.0001) were found to be increased in ID-associated thrombocytosis patients, similarly for each ID. Platelets increase was already found on admission in 18 patients (56%), was mild in most cases (median 492.5 × 109/L, range 401–917 × 109/L) and resolved after recovery in all survivors. The median time to thrombocytosis was 1 day in patients with CAP, 4 days in UTI and 7.5 days in SSTI. No thrombotic complications were found.


      Approximately 8% of patients with acute ID examined had thrombocytosis which was mostly mild, transient, and not usually indicative of an infectious complication. However, these patients had enhanced acute-phase response, increased length of hospital stay, more bacteremia and increased mortality/suppurative complications albeit affecting a minority of patients.


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