Diagnostic and prognostic value of thrombocytosis in admitted medical patients

Introduction: Whether secondary thrombocytosis is a distinguishing clinical biomarker of various diseases, and whether it is an independent predictor of short-term outcome of admitted medical patients is unknown and has never been examined. Methods: A cohort of all 138 patients with secondary thrombocytosis (platelets count ≥ 5 × 105/μL) admitted to the department of medicine during the last 2 years was analyzed. Epidemiological and clinical data, and the final diagnosis and outcome were recorded and compared with a cohort of 684 consecutive admitted patients without thrombocytosis. Results: Thrombocytosis was not a non-specific marker of inflammation, because uncomplicated infections and most admission causes were not associated with thrombocytosis, except for inflammatory rheumatic diseases (6% versus 1%), along with anemia (9.4% versus 2.5%) and tumor comorbidity (25% versus 14%). In contrast, thrombocytosis was a distinguishing biomarker for severe pyogenic infections, especially empyema (5% vs. 0%), any abscesses (14% versus 3%), and soft tissue infections (7% versus 3%). Moreover, the thrombocytosis group had significantly more admission days, infections (45% versus 33%), sepsis (21% versus 6%), in-hospital major complications (15% versus 3%) and mortality (19% versus 5%). Finally, thrombocytosis was found to be an independent predictor of mortality, in a multivariate regression analysis. Conclusions: Thrombocytosis is not a simple marker of inflammation. Its presence warrants thorough investigation for the presence of severe underlying disease, mostly complicated pyogenic infections, inflammatory rheumatic diseases and malignancy. Moreover, thrombocytosis is a marker for major complications and is an independent predictor of mortality in admitted medical patients.