(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 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
Severe lung disease, such as COPD (chronic obstructive pulmonary disease)
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 at birth and resulting in secondary erythrocytosis.
Other causes of secondary erythrocytosis include
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 they 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, and the use of drugs that speed elimination of salt and water by the kidneys (diuretics)
Doctors ask about any drugs that may cause erythrocytosis. They measure the amount of oxygen and the level of erythropoietin in the blood. A high level of erythropoietin is often enough for doctors to diagnose secondary erythrocytosis. If the level is low, other tests for the primary erythrocytosis (polycythemia vera) will be done.
Sometimes other specialized tests are done, especially when doctors need to determine an uncommon cause of erythrocytosis. These may include tests to look for a hormone disorder or a hidden tumor that might be causing other symptoms.
Congenital erythrocytosis is usually diagnosed when a person develops symptoms at an early age or has family members who also have erythrocytosis. In addition to blood tests, doctors may do genetic testing to determine the specific cause.
Secondary erythrocytosis that is caused by oxygen deprivation may be treated with oxygen. Smokers are advised to quit and are offered treatments to assist quitting. Any underlying disorder that is causing the oxygen deprivation and secondary erythrocytosis is treated as effectively as possible. In some people, phlebotomy (in which some of the person's blood is removed) is used to lower the number of red blood cells. It is rare that phlebotomy is needed in secondary erythrocytosis.
In tumor-associated erythrocytosis, removal of the tumor can be curative. Treating a specific hormone disorder or discontinuing a drug that can cause secondary erythrocytosis may also be curative.
Relative erythrocytosis is treated by giving fluids by mouth or intravenously and by treating any underlying conditions that are contributing to the low plasma level.