Diagnosis and Treatment of Erythrocytosis

An erythrocytosis arises when the red cell mass is increased. This can be due to a primary intrinsic defect in the erythroid progenitor cells or secondary to erythropoietin production from some source. Primary and secondary causes can be congenital or acquired. Rare, primary congenital defects are due to mutations leading to truncation of the erythropoietin receptor. The main acquired, primary erythrocytosis is polycythaemia vera. Among the congenital secondary causes, a number of defects in the genes in the oxygen-sensing pathway have recently been described, which lead to a secondary erythrocytosis. An extensive list of acquired secondary causes needs to be considered. A number of patients do not have an identifiable cause of erythrocytosis and are therefore described as having idiopathic erythrocytosis. Investigation should commence with careful clinical evaluation. Determination of the erythropoietin level is then a first step to guide the further direction of investigation. In those with congenital defects, a number of serious thromboembolic events have been described, but there is little information available about outcomes in these individuals and, therefore, no evidence to guide management. In this group, consideration should be given to the use of venesection to attain an achievable haematocrit level, and also low-dose aspirin therapy.