Characteristics of circulating erythroid colony‐forming cells in normal and polycythaemic man

Circulating erythroid progenitors from 10 patients with polycythaemia vera, nine with secondary polycythaemia and 10 normal subjects were studied in culture to determine their frequency, requirements for erythropoietin (ESF) and physical characteristics. Increased numbers of erythroid progenitors were detected in circulation from the patients with polycythaemia vera when compared to patients with secondary polycythaemia or normals, and 19 ± 3% of these progenitors formed endogenous colonies without added ESF. Velocity sedimentation analysis showed that the majority of ESF‐dependent erythroid progenitors in all study groups sedimented at 6.46 mm/h. The circulating endogenous erythroid colony‐forming cells in polycythaemia vera patients sedimented more rapidly. Tritiated thymidine suicide experiments failed to detect significant differences between the percentages of endogenous and ESF‐dependent progenitors in DNA synthesis in polycythaemia patients and normals. Thus, differences in cell cycle state were not responsible for the more rapid sedimentation of endogenous colony‐forming cells. These results further define characteristics of circulating erythroid progenitors in polycythaemia vera and normal subjects and suggest that simple culture of peripheral blood cells may be useful in the differential diagnosis of polycythaemia.