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

Abstract

Background: 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.

Setting: A department of internal medicine in a general teaching hospital.

Methods: 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.

Results: 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.

Conclusions: 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.

Keywords: Erysipelas/cellulitis; Hematology; Infectious diseases; Pneumonia, community-acquired; Thrombocytosis; Urinary tract infection.