Contributor: Gordon K. Klintworth
Secondary polycythemia is a physiological response that can occur at any age in situations in which the blood takes up insufficient oxygen for deliver to different tissues. Conditions associated with this type of polycythemia  include congenital heart disease with right-to-left shunt, pulmonary artery stenosis, emphysema of the lung, Ayerza disease, hemoglobinopathies [hemoglobinopathy] with increased oxygen affinity for the abnormal hemoglobin (methemoglobinemia). A temporary secondary polycythemia occurs when individuals live at a high altitude. Secondary polycythemia results from hypoxia of the kidney causing a release of erythropoietin which increases erythrocyte production. Erythropoietin may also be produced by renal disease (cysts, hydronephrosis) that cause localized renal hypoxia. The erythrocytosis may also be part of a paraneoplastic syndrome in association with a variety of neoplasms (renal cell carcinoma [carcinoma - renal cell],  tumors of the cerebellum [hemangioblastoma], primary hepatocellular carcinoma [carcinoma - hepatocellular] and  uterine leiomyoma). The manifestations of secondary polycythemia resemble those of primary polycythemia, but cyanosis is often more pronounced in secondary polycythemia. In both primary polycythemia and secondary polycythemia a hyperviscosity of the blood occurs when the erythrocyte count becomes markedly elevated (usually >6 million/mm3). Ophthalmic manifestations of polycythemia include cyanosis of the fundus, engorged veins in the retina with marked stasis, retinal hemorrhages [hemorrhage - retina], swelling of the optic nerve head, central retinal artery occlusion and central retinal vein occlusion. Secondary polycythemia needs to be differentiated from primary polycythemia [polycythemia - primary].