Idiopathic erythrocytosis, diagnosis and clinical management.

By definition, idiopathic erythrocytosis (IE) applies to a group of patients characterised by having a measured RCM above their predicted normal range (an absolute erythrocytosis) and following investigation do not have a form of primary or secondary erythrocytosis. Patients with IE are heterogenous. The possibilities include physiological variation, 'early' polycythaemia vera (10-15% develop clear features of PV over a few years), unrecognized congenital erythrocytosis, unrecognized or unrecognizable secondary acquired erythrocytosis or a currently undescribed form of primary or secondary erythrocytosis. Patients are more commonly male with a median age at presentation of 55-60 years. Approximately half of the patients present with vascular occlusive complications. Retrospective evidence indicates that vascular occlusion occurs less frequently when the PCV is controlled at normal levels. Venesection is the treatment of choice to lower the PCV. As a general approach to management, all patients with a PCV above 0.54 should be venesected to a PCV less than 0.45. This target PCV should also apply to patients with lesser degrees of raised PCV who have additional other risk factors for vascular occlusion.