What is the pathophysiology of secondary polycythemia?

Updated: Jul 20, 2020
  • Author: Srikanth Nagalla, MBBS, MS, FACP; Chief Editor: Sara J Grethlein, MD, FACP  more...
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Answer

Increased hemoglobin and hematocrit values reflect an increase in the ratio of red blood cell mass to plasma volume. Any change in either the hemoglobin or the hematocrit can alter test results.

Relative polycythemia, or erythrocythemia, results from decreased plasma volume. A true polycythemia or erythrocythemia results from increased red blood cell mass. Therefore, hemoglobin and hematocrit levels alone cannot accurately help make this distinction. Direct measurement of red blood cell mass is necessary to differentiate these conditions.

In primary polycythemia, the disorder results from a mutation expressed within the hematopoietic stem cell or progenitor cells, which drives the overproduction and accumulation of red blood cells. The secondary polycythemic disorders may be acquired or congenital; however, they are driven by factors that are independent of the function of hematopoietic stem cells. Elevated hemoglobin levels due to chronic hypoxia in patients with chronic lung disorders such as COPD or sleep apnea are the result of an increased production of erythropoietin, which in turn causes increased production of red blood cells. 


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