APPARENT POLYCYTHEMIA - DIAGNOSIS, PATHOGENESIS AND MANAGEMENT

The term ''apparent polcythaemia'' is applied to a group of patients w ho have a raised PCV (>0.51 in males, >0.48 in females) but a normal r ed cell mass (less than 25% above their predicted mean normal value). Some have additionally a marked reduction inn plasma volume and can be defined as a subgroup: relative polycythaemia. Smoking, hypertension and to a lesser extent obesity, excessive alcohol, low-dose diuretic t herapy and hypoxaemia have all been associated with apparent polythaem ia but the mechanism is both uncertain and likely to be complex. This group of patients is unlikely to be uniform in pathogenesis and may we ll include some normal individuals. Investigation requires exclusion o f factors associated with other types of polycythaemia. The possibilit y of an increased vascular occlusive risk is uncertain in these patien ts except at the higher PCV values. Reduction of PCV by venesection is sensible at PCV > 0. 54 or where there is perceived to be an increase d risk of vascular occlusion. The remaining patients should be managed by regular observation to detect further rise in PCV or evolution to absolute polycythaemia (raised red cell mass). In some, the PCV return s to normal.