A research team performed a chart review to determine common etiologies of extreme thrombocytosis (EXT), and they found significant differences arising in inpatient versus outpatient settings. The study results were published in Mayo Clinic Proceedings.

For this retrospective analysis, the researchers examined Mayo Clinic records of 44,490 adult patients with evidence of thrombocytosis. Patients with 2 or more reports of platelet counts higher than 1000 x 109/L within a 30-day period were considered to have EXT. Study inclusion dates were January 1, 2011, through December 31, 2016.

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EXT was found in 305 patients, 79.3% of whom exhibited multifactorial EXT. A total of 196 were inpatients and 109 were outpatients. EXT was resolved within 30 days in 84% of cases among 288 patients for whom such data were available.

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Among inpatients, EXT could most often be attributed to surgical complications (71.9%), asplenia (50.5%), and infections (44.9%). For outpatients, the primary contributors to EXT were hematologic malignancies (56.9%), followed by asplenia (36.7%) and iron deficiency (28.4%).

In the overall population, surgical complications were the main cause of EXT in 54.1% of patients, while hematologic malignancy was the primary cause in 27.9% of patients. Infections or inflammation, asplenia, and iron deficiency typically were not primary causes of EXT.

Myeloproliferative neoplasms were the most common hematologic malignancies to be diagnosed among patients in this analysis. Although hematologic malignancies were at times a driver of EXT, new cancer diagnoses occurred in only 12.5% of cases of EXT overall.

The researchers proposed an algorithm for diagnosis and treatment of EXT. “We recommend a bone marrow evaluation only if none of the major causes — recent surgery, active infection, history of splenectomy, and myeloproliferative neoplasms — are present at the time of EXT evaluation,” the authors stated.


  1. Hsieh RW, Ravindran A, Hook CC, et al. Etiologies of extreme thrombocytosis: a contemporary series. Mayo Clin Proc. 2019;94(8):1542-1550.