Secondary Erythrocytosis

Erythrocytosis is increased production of red blood cells (erythrocytes).

(See also Overview of Myeloproliferative Neoplasms.)

Erythrocytosis may be

• Primary: Caused by a disorder of the blood-forming cells

• Secondary: Caused by a disorder that triggers increased production by normal blood-forming cells

Primary erythrocytosis occurs as a result of polycythemia vera, a myeloproliferative neoplasm in which abnormal cells in the bone marrow produce too many red blood cells along with excessive numbers of white blood cells and platelets. Occasionally, only red blood cell production is increased.

Secondary erythrocytosis develops generally as a result of a disorder that increases erythropoietin secretion. Erythropoietin is a hormone made in the kidneys that stimulates the bone marrow to produce red blood cells. As such, secondary erythrocytosis is not considered a myeloproliferative neoplasm. However, it is important for doctors to look for it because both primary and secondary erythrocytosis result in too many red blood cells.

Secondary erythrocytosis has many causes. It can be caused by oxygen deprivation, which can result, for example, from

• Smoking

• Severe lung disease, such as COPD (chronic obstructive pulmonary disease)

• Birth defects of the heart

• Carbon monoxide poisoning

• High altitude

Oxygen deprivation causes an increase in erythropoietin, which stimulates the bone marrow to produce more red blood cells so that the blood can carry more oxygen. People who spend long periods of time in environments or circumstances low in oxygen, such as people who live at high altitude, often develop erythrocytosis severe enough to cause symptoms (see What is Chronic Mountain Sickness?). In some birth defects of the heart, blood is misdirected away from the heart so that it cannot pick up oxygen, causing hypoxia (a low level of oxygen in the blood) and resulting in secondary erythrocytosis.

Other causes of secondary erythrocytosis include

• Treatment with male hormones such as testosterone

• Kidney problems, including tumors, cysts, and narrowing of the arteries that go to the kidneys

• Tumors of the liver, brain, or adrenal gland

• Genetic disorders that affect erythropoietin production (congenital erythrocytosis)

Male hormones such as testosterone stimulate production of erythropoietin.

Problems that decrease blood flow to the kidneys such as tumors, cysts, and narrowing of the arteries that go to the kidneys increase erythropoietin secretion.

Tumor-associated erythrocytosis can occur when certain tumors or cysts, such as of the kidneys, liver, brain, or uterus secrete erythropoietin.

Congenital erythrocytosis is present at birth and is usually caused by an inherited genetic disorder that affects the affinity of hemoglobin for oxygen or the response to hypoxia. (Hemoglobin is the molecule that carries oxygen within red blood cells. Hypoxia is when the level of oxygen in the blood is low.) These inherited genetic disorders are rare, but they are suspected when a person with erythrocytosis has family members who are also affected.

In relative erythrocytosis, there are not any extra red blood cells, but red blood cells seem to be at a high concentration because there is less fluid (plasma) in the bloodstream. The low plasma level can result from burns, vomiting, diarrhea, drinking an inadequate amount of fluids, or the use of medications that speed elimination of salt and water by the kidneys (diuretics).