Megakaryocyte and erythroid colony formation in essential thrombocythaemia and reactive thrombocytosis: diagnostic value and correlation to complications.

Megakaryocyte and erythroid colony formation in vitro by progenitors from the bone marrow and/or blood was studied in 61 patients with essential thrombocythaemia (ET) and 22 patients with reactive thrombocytosis (RT) using the methyl cellulose assay. 47 (77%) of the patients with ET showed megakaryocyte and/or erythroid spontaneous colony formation while 14 (23%) patients did not have any kind of spontaneous colonies. Spontaneous megakaryocyte colony formation was seen in 42 (69%) of the patients and 36 (59%) ET patients showed spontaneous erythroid growth. 31 patients had both types of spontaneous colonies. 11 patients showed only spontaneous megakaryocyte colony formation, and five patients only spontaneous erythroid growth. None of the patients with RT or of the normal controls showed either type of spontaneous growth. Neither the presence of spontaneous megakaryocyte colony formation nor the number of spontaneous colonies correlated with the platelet count. Patients with spontaneous megakaryocyte growth had significantly more often thromboembolic or haemorrhagic problems than those without spontaneous colony formation. In conclusion, it was found that a great majority of patients with ET but none of those with RT grow spontaneous megakaryocyte and/or erythroid colonies. Spontaneous colony formation is strong evidence for a myeloproliferative disorder. The presence of spontaneous colony growth is associated with an increased risk of thromboembolic or haemorrhagic complications regardless of the platelet count, particularly among young patients.