Congenital and acquired polycythemias.

INTRODUCTION: Polycythemias are characterized by an increased concentration of red blood cells. Because blood cell counts are a routine investigation, these disorders present to non-hematologic physicians. Polycythemia vera (PV), an acquired stem cell disease, is the most important variant.
METHODS: Selective literature review and the authors' own clinical experiences. RESULTS AND DISCUSSION: Erythropoietin, which is produced in the kidneys, and its receptor system in the bone marrow, are of critical importance in polycythemia. Congenital polycythemias are caused by mutations of the Erythropoietin-receptor gene, hemoglobin variants, 2,3-bisphosphoglycerate mutase deficiency or by disturbances of renal oxygen sensing. Acquired polycythemias can occur secondary to hypoxia at high altitudes, or primarily through acquired mutations in the EPO-receptor signaling system (JAK2 mutations). Alternatively they may be caused by pulmonary or renal disease. An artificial erythrocytosis is induced by athletes through doping. Differential diagnosis comprises erythropoietin determination, JAK2 mutation analysis and if necessary hemoglobin electrophoresis. Only PV requires immediate treatment, because of a high thromboembolic risk. Epidemiological studies on polycythemias in German speaking countries are urgently needed.