1. Patients with polycythemia vera may be classified according to their erythropoietic pattern. Erythropoiesis is abnormally increased in all classes. Class I is characterized by normal red cell lifespan. Class II is characterized by shortened red cell lifespan; in Class IIa the shortened red cell survival is related to splenic sequestration of RBC; in Class IIb the markedly shortened red cell survival is predominantly related to intramedullary hemolysis. Class III is characterized by extramedullary erythropoiesis. Patients in Classes I and IIa are in relatively earlier phases of their disease and frequently are found to develop red cell kinetics of Class III as their disease progresses. Conversely, patients in Classes IIb and III are generally late in the course of their disease and have previous hematologic findings that suggest that they originally had the red cell kinetic patterns of Classes I and IIa.
2. As the duration of their disease increases, patients with polycythemia vera generally have a progressive shortening of red cell lifespan which is incompletely compensated by a progressive decrease in circulating red cell volume. However, total blood volume remains elevated since the plasma volume increases. These changes occur whether or not the patient receives radiation therapy. Similar changes may occur in white cell and platelet production and functional survival. It is suggested that the natural history of the disease may be characterized by progressive emergence of hematopoietic cell clones which have a selective advantage for reproduction associated with altered functional survival.
3. The results suggest the potential usefulness of iron, and occasionally of splenectomy, in selected polycythemic patients with myeloid metaplasia (Class III) and anemia, dependent upon the presence of the frequent finding of iron deficiency or the occasional finding of splenic sequestration of red cells in excess of splenic erythropoiesis.