Secondary Polycythemia

Excerpt

Polycythemia, derived from poly (many) and cythemia (cells in the blood), is a condition defined as an abnormal increase in the red blood cell (RBC) mass. For a normal healthy adult, the RBC mass is 23 to 29 mL/kg in females and 26 to 32 mL/kg in males. Patients with hematocrit values greater than 51% and 48% and hemoglobin values greater than 185g/L and 165 g/L in males and females, respectively, usually have an elevated RBC mass. Polycythemia is not synonymous with erythrocytosis. Absolute erythrocytosis is defined as an RBC mass greater than 125% of the predicted value adjusted for gender and body weight.

Absolute or true erythrocytosis differentiates from relative polycythemia, where the hematocrit is increased, but the red cell mass lies within the normal range. The elevated hematocrit can be due to the contracted plasma volume.

An elevated erythropoietin (EPO) level, usually as a secondary response to chronic hypoxemia, leads to secondary polycythemia. Chronic hypoxemia can be secondary to various conditions, including lung pathologies like chronic obstructive pulmonary disease (COPD), airway pathologies like obstructive sleep apnea as well as muscular abnormalities like obesity hypoventilation syndrome.