Aetiology and clinical significance of thrombocytosis: analysis of 732 patients with an elevated platelet count

Objective. To determine the aetiology and clinical significance of an eleva ted platelet count (thrombocytosis) in a large cohort of patients. Design. A retrospective review of the medical records was performed on all patients, who had at least, one platelet count greater than or equal to 500 x 10(9) L-1 Setting. Departments of Medicine and Surgery, University of Ulm, Germany, Subjects, A total of 732 patients with thrombocytosis. Main outcome measures. Classification of thrombocytosis and thromboembolic complications, and evaluation of laboratory parameters distinguishing betwe en primary and secondary thrombocytosis, Results. Of the total of 732 patients, 89 (12.3%) had primary and 643 (87.7 %) had secondary thrombocytosis, Essential thrombocythaemia was observed in 40 of 89 patients (45%) with primary thrombocytosis. The most frequent cau ses of secondary thrombocytosis were tissue damage (42%), infection (24%), malignancy (13%) and chronic inflammation (10%), Primary thrombocytosis was significantly associated with a higher platelet count and an increased inc idence of both arterial and venous thromboembolic complications, In seconda ry thrombocytosis, thromboembolic events were restricted to the venous syst em and occurred only in the presence of other risk factors. Mean values of leucocyte count, haematocrit, erythrocyte sedimentation rate, fibrinogen, s erum potassium and lactate dehydrogenase were significantly different in pr imary and secondary thrombocytosis. Conclusions. The finding of an elevated platelet count on routine blood exa mination has diagnostic, prognostic and therapeutic implications. It is of clinical importance to distinguish between primary and secondary thrombocyt osis, as thrombotic complications occur more frequently in primary thromboc ytosis. Unless additional risk factors are present, secondary thrombocytosi s is not associated with a significant risk for thromboembolic events.