Polycythemia, Secondary

Also known as reactive polycythemia, secondary polycythemia is a disorder characterized by excessive production of circulating red blood cells (RBCs) due to hypoxia, tumor, or disease. It occurs in approximately 2 out of every 100,000 people living at or near sea level; incidence rises among persons living at high altitudes.

Causes

Polycythemia may be caused by the following:

• increased red blood cell production:
  
  • A fetus with chronically lowered oxygen levels responds by producing extra red blood cells.
  • Some chromosomal abnormalities may cause increased red blood cell production.
    
• extra blood cells enter the baby's circulation from another source:
  
  • A delay in clamping the umbilical cord after delivery results in blood from the placenta entering the baby's circulation.
  • Twin-to-twin transfusion, when the shared placenta of the two babies has a connecting circulation and blood flows from one baby to the other, may result in polycythemia.

Signs and symptoms

In the hypoxic patient, suggestive physical findings include ruddy cyanotic skin, emphysema, hypoxemia without hepatosplenomegaly, or hypertension. Clubbing of the fingers may occur if the underlying disease is cardiovascular. When the cause isn't hypoxemia, secondary polycythemia is usually an incidental finding during treatment for an underlying disease.

Diagnosis

Laboratory findings for secondary polycythemia include increased RBC mass (increased hematocrit, hemoglobin, mean corpuscular volume, and mean corpuscular Hb), urinary erythropoietin, and blood histamine, with decreased or normal arterial oxygen saturation.

Bone marrow biopsies reveal hyperplasia confined to the erythroid series. Unlike polycythemia vera, secondary polycythemia isn't associated with leukocytosis or thrombocytosis.

Treatment

The goal of treatment is correction of the underlying disease or environmental condition. In severe secondary polycythemia where altitude is a contributing factor, relocation may be advisable. If secondary polycythemia has produced hazardous hyperviscosity of the blood or if the patient doesn't respond to treatment for the primary disease, reduction of blood volume by phlebotomy or pheresis may be effective.

Emergency phlebotomy is indicated for prevention of impending vascular occlusion or before emergency surgery. In the latter case, it's usually advisable to remove excess RBCs and reinfuse the patient's plasma.

Prognosis

Curing or removing the underlying cause of this disorder generally eliminates the symptoms.