Secondary Polycythemia

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

Practice Essentials

In secondary polycythemia, the number of red blood cells (RBCs) is increased as a result of an underlying condition. Secondary polycythemia would more accurately be called secondary erythrocytosis or erythrocythemia, as those terms specifically denote increased red blood cells. The term polycythemia is used appropriately in the myeloproliferative disorder called polycythemia vera, in which there are elevated levels of all three peripheral blood cell lines—RBCs, white blood cells, and platelets. [1, 2]

Secondary polycythemia most often develops as a response to chronic hypoxemia, which triggers increased production of erythropoietin by the kidneys. The most common causes of secondary polycythemia include obstructive sleep apnea, obesity hypoventilation syndrome, and chronic obstructive pulmonary disease (COPD). [3] Other causes include testosterone replacement therapy [4] and heavy cigarette smoking. Patients who have arteriovenous or intracardiac shunting can present with polycythemia without hypoxemia. Erythropoietin-secreting tumors (eg, hepatocellular carcinoma, renal cell carcinoma, adrenal adenoma) cause some cases.

Secondary polycythemia must be differentiated from primary polycythemia and relative polycythemia (in which RBC numbers are normal but plasma volume is contracted. The reduction in plasma volume may be due to dehydration or to reduced venous compliance; the latter is also termed stress polycythemia or Gaisböck syndrome, and is typically seen in obese middle-aged men who are receiving a diuretic for treatment of hypertension. See Presentation and Workup.

To the extent that the increased RBCs alleviate tissue hypoxia, secondary polycythemia may in fact be beneficial. However, treatment with phlebotomy is indicated for patients with hematocrits higher than 60%-65%, who may experience symptoms such as  impaired alertness, dizziness, headaches, and compromised exercise tolerance, and who may face increased risk for thrombosis, strokes, myocardial infarction, and deep venous thrombosis. Otherwise, secondary polycythemia is addressed by treating the underlying condition. See Treatment.

 

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Pathophysiology

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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Epidemiology

The frequency of secondary polycythemia depends on the underlying disease. The mortality and morbidity of secondary polycythemia depend on the underlying condition.

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Prognosis

The prognosis of patients with secondary polycythemia is driven by the underlying disorder. In general, patients with secondary polycythemia have a shorter survival following diagnosis than patients with polycythemia vera. This is believed to reflect the dire underlying conditions that may result in secondary polycythemia.

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