An increase in the platelet count may be primary (due to a myeloproliferative disorder, myelodysplasia, or leukemia) or secondary (reactive). A careful evaluation of the patient can identify the cause in most patients, but some patients may need to be followed over time.


Causes of secondary thrombocytosis:

(1) acute inflammatory response (due to infection, autoimmune disease, etc)

(2) non-hematologic malignancy

(3) post-splenectomy or with hyposplenism

(4) hemorrhage

(5) iron deficiency anemia

(6) following a surgical procedure

(7) following trauma

(8) rebound proliferation following chemotherapy

(9) rebound proliferation following therapy for vitamin B12 or folate deficiency


General features suggesting a secondary thrombocytosis:

(1) identifiable cause

(2) either transient or reverses after underlying cause is treated

(3) associated with elevation of acute phase reactants

(4) not associated with hypercoagulability (exceptions may be non-hematologic malignancy and bedrest after trauma or surgery)


The diagnosis of thrombocytosis can be challenging if both primary and secondary thrombocytosis are present.


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