Polycythemia (High Red Blood Cell Count)

Polycythemia
(Elevated Red Blood Cell Count)

Medical Author: Siamak Nabili, MD, MPH
Medical Editor: Charles Davis, MD, PhD

• What is polycythemia?
• What are normal ranges of hematocrit, red cell counts, and hemoglobin?
• What causes polycythemia?
• What are the causes of primary polycythemia?
• What are the common causes of secondary polycythemia?
• Can other sources of erythropoietin (EPO) cause polycythemia?
• What is relative polycythemia?
• What is stress polycythemia?
• What are the risk factors for polycythemia?
• What are the symptoms of polycythemia?
• When should I see a doctor about polycythemia?
• How is polycythemia diagnosed?
• What is the treatment for polycythemia?
• What are the complications of polycythemia?
• Can polycythemia be prevented?
• What is the outlook (prognosis) for polycythemia?
• Polycythemia At A Glance

What is polycythemia?

Polycythemia is a condition that results in an increased level of circulating red blood cells in the bloodstream. People with polycythemia have an increase in hematocrit, hemoglobin, or red blood cell count above the normal limits.

Polycythemia is normally reported in terms of increased hematocrit or hemoglobin.

• Hematocrit (HCT): Polycythemia is considered when the hematocrit is greater than 48% in women and 52% in men.
  
  
• Hemoglobin (HGB): Polycythemia is considered when a hemoglobin level of greater than 16.5g/dL in women or hemoglobin level greater than18.5 g/dL in men.

Polycythemia can be divided into two categories; primary and secondary.

• Primary polycythemia: In primary polycythemia the increase in red blood cells is due to inherent problems in the process of red blood cell production.
  
  
• Secondary polycythemia: Secondary polycythemia generally occurs as a response to other factors or underlying conditions that promote red blood cell production.

Red cell production (erythropoiesis) takes place in the bone marrow through a complex sequence of tightly regulated steps. The main regulator of the red cell production is the hormone erythropoietin (EPO). This hormone is largely secreted by the kidneys, although, about 10% may be produced and secreted by the liver.

Erythropoietin secretion is up-regulated in response to low oxygen levels (hypoxia) in the blood. More oxygen can be carried to tissues when erythropoietin stimulates red blood cell production in the bone marrow to compensate for the hypoxia.

Neonatal (newborn) polycythemia can be seen in 1% to 5% of newborns. The most common causes may be related to transfusion of blood, transfer of placental blood to the infant after delivery, or chronic inadequate oxygenation of the fetus (intrauterine hypoxia) due to placental insufficiency.