Increase in red blood cell concentration secondary to chronic tissue hypoxia, as seen in cyanotic CHD and in chronic pulmonary disease. It results from a hypoxia-induced physiologic response resulting in increased erythropoeitin levels, and affects only the red cell line. It is also called secondary erythrocytosis. The term "polycythemia" is inaccurate in this context, since other blood cell lines are not affected. see also polycythemia vera. Erythrocytosis may cause hyperviscosity symptoms. see also hyperviscosity.
