Journal Mobile

DJ Culligan
Journal Issue: 
Volume 38: Issue 4: 2008




Erythrocytosis and thrombocytosis are among the most common reasons for referral to haematology outpatients. Most cases are identified on routine blood counts as part of the investigation of non-specific symptoms. Erythrocytosis is a term used  to  describe  a  group  of  conditions  with  an  increase  in  circulating  red  cell concentration  leading  to  an  increase  in  haematocrit  and  often  an  increase  in haemoglobin  concentration  (polycythaemia). True  erythrocytosis  is  commonly  seen in isolation but may also be associated with thrombocytosis and leukocytosis in the myeloproliferative disease polycythaemia vera (PV). Isolated erythrocytosis may also be a manifestation of myeloproliferative disease but is commonly seen as a secondary response  to  elevated  erythropoietin  levels,  most  frequently  because  of  chronic hypoxia. Recently, an acquired point mutation in the gene Janus kinase 2 (JAK2) has been  identified  in  approximately  95%  of  cases  of  PV,  and  this  is  a  significant development  in  terms  of  diagnosis  and  as  a  future  target  for  therapy.  Persistent thrombocytosis  is  the  hallmark  of  another  myeloproliferative  disease:  essential thrombocythaemia  (ET). The  same  acquired  point  mutation  in JAK2 is  identified  in approximately  40–50%  of  cases  of  ET. Transient  reactive  thrombocytosis  (days  to months) is a common response to a wide range of conditions including acute and chronic  blood  loss,  iron  deficiency,  malignancy,  sepsis,  chronic  inflammation  and temporal arteritis. The identification of the myeloproliferative forms of erythrocytosis and thrombocytosis is important as appropriate therapy will reduce the lifetime risk of arterial and venous thromboembolic disease.