Circulating erythroid and megakaryocytic progenitors in polycythaemia vera and essential thrombocythaemia.

We studied the behaviour in culture of erythroid and megakaryocyte progenitor cells (BFU-E, CFU-MK) obtained from peripheral blood (PB) in 38 patients: 15 with essential thrombocythaemia, 3 with reactive thrombocytosis, 16 with polycythaemia vera and 4 with secondary polyglobulia. Clonal erythroid growth without added erythropoietin was observed in all patients with polycythaemia vera and in 5 out of 15 with essential thrombocythaemia, but in none of the patients with reactive thrombocytosis or secondary polyglobulia or in controls. When the CFU-MK were cultured without phytohaemagglutinin-stimulated medium (PHA-LCM), all patients with essential thrombocythaemia and 7 out of 16 with polycythaemia vera showed circulating CFU-MK but none of those with reactive thrombocytosis or secondary polyglobulia or controls did so. This study indicates that the growth in vitro of megakaryocytic and erythroid progenitors from such a readily available source as peripheral blood can be valuable in the diagnosis of certain borderline cases of thrombocytosis or erythrocytosis.