What is the difference between primary and secondary thrombocytosis?

By William Aird

Primary thrombocytosis is caused by a clonal disorder of hematopoietic stem cells or by inherited mutations (familial or congenital thrombocytosis). Secondary or reactive thrombocytosis occurs when signals (often cytokines like IL-11) promote proliferation and differentiation of normal megakaryocytes. Learn more here.

Mechanisms of thrombocytosis. Primary or clonal thrombocytosis involves autonomous growth of stem cells or megakaryocyte progenitor cells owing to mutations in genes involved in cell growth and differentiation/maturation. In these cases, the megakaryocyte progenitors are impervious to normal inhibitory signals and proliferate uncontrollably. In secondary (reactive) thrombocytosis, the megakaryocytes are perfectly normal. They are simply marching to the tune of the microenvironment, dividing and differentiating in response to extracellular signals such as thrombopoietin and interleukn-6. Finally, the spleen normally pools about one-third of the circulating mass of platelets. When it is removed, or it is hypofunctioning, the sponge effect of the spleen is lost and platelet counts may increase.