Viera Fábryová
Increased haemoglobin and hematocrit values reflect the ratio of red blood cells mass to plasma volume. In true erythrocytosis results absolutely increased red blood cells mass is concerned. In primary polycythaemia, the disorder results from a mutation expressed within the hematopoietic stem cells or progenitor cells, which leads to the eventual accumulation of red blood cells. The secondary erythrocytosis may be acquired or congenital; however it is driven by circulating factors that are independent of the function of hematopoietic stem cells. Relative erythrocytosis results from decreased plasma volume. Idiopathic erythrocytosis is a term reserved for cases where primary polycythaemia or secondary erythrocytosis was not confirmed. Correct and rapid diagnosis of elevated haemoglobin and hematocrit values plays an important role in the initiation of an adequate treatment.