thrombocytosis can be physiologic (exercise, parturition) and can also be
primary/clonal (e.g., essential thrombocythemia, polycythemia vera, primary
myelofibrosis, and other hematologic malignancies) as well as secondary/
reactive (due to infectious and inflammatory diseases, neoplasms, anemia,
trauma, surgery, asplenia, and iron deficiency).
In the ED, we must try to differentiate myeloproliferative/clonal thrombocytosis from secondary/reactive thrombocytosis.
Thrombocytosis is a risk marker of cancer in adults; 11.6% and 6.2% cancer incidence in males and females, respectively, is worthy of further investigation for underlying malignancy.
In managing the patient with thrombocytosis, one must first distinguish reactive from primary thrombocytosis. The presence of acute or subacute infection, a connective tissue disorder, vasculitis, hemolysis, active bleeding, recent surgery, history of splenectomy, or iron deficiency anemia favors the diagnosis of reactive thrombocytosis.
Thrombocytosis is very common and is often transient in children when it is a secondary thrombocytosis. Primary (or essential thrombocytosis) is less common in children. It is better understood in adults where it is part of the family of myeloproliferative neoplasms and can cause complications.
Thrombocytosis is defined as a platelet count exceeding 450 × 109/L in adults.1,2 This abnormality is classified as “primary thrombocytosis,” when the increase in platelets is caused by alterations targeting the hematopoietic cells, or as “secondary thrombocytosis” (also called “reactive thrombocytosis”), when the increase in platelets can be traced to an external cause, such as chronic inflammation, cancer, iron deficiency, or rebound after splenectomy.
Thrombocytosis is defined as a platelet count above 350,000 to 400,000/μL, which is the upper limit of the normal reference range. Thrombocytosis may be categorized as familial, reactive, or secondary nonclonal processes (reactive thrombocytosis [RT]), or as the manifestation of a primary myeloproliferative disorder (MPD)—usually an autonomous and clonal process.