[Differential Diagnosis of Erythrocytosis - Background and Clinical Relevance].

Due to its rare incidence, erythrocytosis frequently represents a challenge for the treating doctors. The erythropoiesis (= production of erythrocytes) is located in the bone marrow, and the hormone erythropoietin (EPO) takes control in its regulation. Therefore, measurement of EPO in serum is one of the main diagnostic steps. In erythrocytosis, congenital causes have to be distinguished from acquired ones. Furthermore, there are primary and secondary forms. Congenital causes of erythrocytoses occur very infrequently, are mainly diagnosed in young age and should be treated in specialized centers. Polycythemia vera (PV), a clonal disorder and one of the main myeloproliferative neoplasms (beside essential thrombocythemia and primary myelofibrosis), represents the most frequent primary acquired cause of erythrocytosis. Clinically, increased thrombophilia and microvascular disturbance occur. The first-line treatment in patients with PV includes administration of aspirin and phlebotomies. Secondary acquired forms of erythrocytosis mainly occur due to hypoxia triggered by nicotine abuse or chronic heart and lung diseases. Regarding other differential diagnoses, a cancer-associated EPO production, kidney diseases or exogenous supply with EPO (= EPO doping) have to be considered.