ABSTRACT
The term polycythemia may be used for the condition in all patients with raised hematocrit or packed cell volume values. The absolute polycythemias may be divided into three subgroups. First, there is polycythemia rubra vera or primary proliferative polycythemia, a myeloproliferative disorder where a clonal proliferation replaces the normal marrow tissue. Second, there are the secondary polycythemias, where an increased red cell mass (RCM) results from increased erythropoietin production. Third, there is idiopathic erythrocytosis, probably a heterogenous group where at presentation no underlying cause for the raised RCM can be found, nor are there other hematological features to establish the presence of the clonal disorder, primary proliferative polycythemia. Adaptation to the left-shifted oxygen dissociation curve in the patients involves a number of mechanisms, including those of polycythemia and increased cardiac index.
