Walsh & Hoyt: Erythrocytosis and Polycythemia Vera

Erythrocytosis is characterized by elevation of the red blood cell count, hematocrit, and hemoglobin concentration; it may be absolute or apparent. Absolute erythrocytosis results from an increase in total red cell mass and may be further categorized as clonal and nonclonal. Clonal erythrocytosis results from a disorder intrinsic to the erythroid progenitor cells of the bone marrow, independent of erythropoietin, and is called polycythemia (rubra) vera. Nonclonal or secondary erythrocytosis results from an otherwise normal bone marrow excessively stimulated by erythropoietin elevated by physiologic demand or pathologic production. Apparent erythrocytosis is not accompanied by an increased red cell mass. Instead, it results from decreased plasma volume or an increased ratio of red cell mass to plasma volume. Polycythemia vera is a malignancy of the hemopoietic system characterized by excessive proliferation of erythroid, myeloid, and megakaryocytic elements within the bone marrow, resulting in an increased red blood cell mass, low serum erythropoietin and, frequently, elevated peripheral granulocyte and platelet counts.