Polycythemia is defined by the increase of hematocrit and haemoglobin respectively. Possible causes might be neoplastic diseases like polycythemia vera with proliferation of a cell clone. More often one will find reactive forms resulting from chronic hypoxemia. A physiologic form of polycythemia can be found in highlanders and athletes training at high altitude. With increasing frequency erytrhopoetin and it's analoga are being used as doping substances to induce Polycythemia. Red cell proliferation induced by chronic hypoxemia is the most common form in patients. In this instance the lung itself can be the cause (hypoxemia with hypocapnea in blood gas analysis) or hypoventilation caused by an insufficient respiratory pump (hypercapnea with hypoxemia in blood gas analysis) induces a compensatory Polycythemia. The former form can be treated with long term oxygen therapy and the latter by non-invasive ventilation, either approach corrects hypoxemia and reduces Polycythemia within some weeks.
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