Polycythemia is defined as an abnormal increase in red blood cell mass, and it is classified mechanistically by whether the defect lies in the erythroid marrow itself or in the upstream hormonal signal that drives it. Primary polycythemia (polycythemia vera) arises from hyperfunctioning of the erythropoietin receptor's JAK-STAT signal transduction pathway in bone marrow progenitors, amplifying the intracellular response to normal erythropoietin binding, whereas secondary polycythemia arises from excess erythropoietin production by renal proximal convoluted tubule cells, typically driven by hypoxia or by autonomous hormone secretion from renal neoplasia. The concept sits within hematology and hematopoietic physiology, and connects to endocrine regulation of erythropoiesis, hemorheology, and thrombosis, since any elevation of red cell concentration raises blood viscosity and thereby peripheral resistance, blood pressure, and thromboembolic risk.
Polycythemia is defined as an abnormal increase in red blood cell mass, and it is classified mechanistically by whether the defect lies in the erythroid marrow itself or in the upstream hormonal sign…