2007.11.23 – Merck_Manual
The Merck Manual of Health & Aging
Polycythemia With an Identifiable Cause
Sometimes the body produces too many red blood cells, and no cause can be identified. This disorder is called polycythemia vera. When a cause can be identified, the disorder is called secondary polycythemia.
Secondary polycythemia can result from the following:
* Conditions that prevent the body’s tissues from getting enough oxygen. Examples are smoking, spending time at a high altitude, and having a severe lung disorder or heart failure.
* Conditions that reduce the amount of fluid (plasma) in the blood. In such cases, the percentage of red blood cells in the blood (hematocrit) increases even though the number is normal. These conditions include burns, vomiting, diarrhea, and use of drugs that increase the amount of salt and water excreted by the kidneys (diuretics). Not drinking enough fluids can also reduce the amount of plasma in the blood.
* Cysts in the kidneys or tumors in the kidneys, liver, or brain that produce erythropoietin. Erythropoietin is a hormone that stimulates the bone marrow to produce red blood cells. These cysts and tumors are rare.
Symptoms of secondary polycythemia are similar to those of polycythemia vera but are usually much milder.
If possible, the condition causing polycythemia is corrected or treated. Depending on the cause, oxygen given by nasal prongs, phlebotomy, or fluids given by mouth or intravenously may be appropriate. Smokers are advised to stop smoking and are offered specific treatment to help them. People who live at high altitudes may be advised to move to lower altitudes if possible.
Generally, the outlook for people with secondary polycythemia is much better than for those with polycythemia vera. Secondary polycythemia, unlike polycythemia vera, does not progress to leukemia.
In polycythemia, too many red blood cells are produced. Polycythemia vera is polycythemia with no identifiable cause. The blood becomes thicker, blood flows less easily through small blood vessels, and blood clots are more likely to form.
Polycythemia vera is relatively uncommon. The average age at which the disorder is diagnosed is 60. Polycythemia vera is more common among men.
In many people with polycythemia vera, too many platelets and too many white blood cells are also produced. Sometimes excess blood cells are produced by the spleen and liver as well as by the bone marrow. As a result, these organs enlarge. Polycythemia vera makes the spleen enlarge in another way. Normally, the spleen removes abnormal, old, or damaged red blood cells. In polycythemia vera, the spleen has to remove more and more red blood cells from the bloodstream.
Polycythemia vera progresses slowly. After many years, it may progress to myelofibrosis. Rarely, it progresses to leukemia. If not treated, polycythemia vera can become life threatening.
The cause of polycythemia vera is, by definition, unknown. If the cause of polycythemia can be identified, it is called secondary polycythemia.
Many people do not have any symptoms for many years. Usually, the first symptoms are weakness, fatigue, headache, light-headedness, shortness of breath, and night sweats. Vision may be affected. People may have blind spots or see flashes of light. The gums may bleed, and small cuts may bleed more than expected. The skin, especially the face, often looks red. People may itch all over, particularly after bathing or showering. The hands and feet may tingle or feel as if they are burning. Rarely, pain is felt in the bones.
The abdomen may feel uncomfortably full because the liver and spleen enlarge. Abdominal pain may result if thickened blood or blood clots interfere with blood flow to the lining of the stomach and causes it to erode. This erosion may lead to ulcers.
Other symptoms can result if a clot blocks a large or crucial blood vessel.
Polycythemia may be diagnosed during routine blood tests, even before a person has any symptoms. The percentage of red blood cells in the blood (hematocrit) and the amount of hemoglobin, which is the protein that carries oxygen in red blood cells, are abnormally high. The platelet and white blood cell count may also be high.
A high hematocrit usually indicates polycythemia. However, another test to confirm the diagnosis is occasionally needed. In this test, red blood cells are withdrawn, labeled with a very small amount of a radioactive substance, and injected back into the body. The total number of red blood cells in the body (red blood cell mass) can be calculated by checking for radioactive cells in a sample of blood withdrawn after a certain time.
Once polycythemia is diagnosed, doctors determine whether the disorder is polycythemia vera or secondary polycythemia. The person’s medical history may help, but sometimes additional tests are needed. For example, blood tests to measure the level of erythropoietin may be done. The level is very low in polycythemia vera but is normal or high in secondary polycythemia. A bone marrow biopsy may also be done.
Treatment and Outlook
Polycythemia vera cannot be cured. But treatment can control it and reduce the risk of problems, such as the formation of blood clots.
Treatment focuses on reducing the number of red blood cells. The usual way is to remove blood from the body in a procedure called phlebotomy. The procedure is similar to donating blood. A pint of blood is removed every other day until the hematocrit reaches a normal level. The level is kept normal by removing blood every few months, as needed.
Phlebotomy may increase the platelet count, which is often already high because of the polycythemia, and does not reduce the size of an enlarged liver or spleen. So people who undergo phlebotomy may also need drugs to suppress production of platelets. The chemotherapy drug hydroxyurea, given by mouth, is often used. It lowers the platelet count and thus reduces the risk of clots. If hydroxyurea has bothersome side effects or reduces the white blood cell count too much, anagrelide may be used instead. It also lowers the platelet count and reduces the risk of clots.
If phlebotomy is ineffective, interferon-alpha (a drug that affects the immune system) may be given as injections.
Other drugs can help control some of the symptoms. For example, antihistamines can help relieve itching. Aspirin can relieve burning sensations in the hands and feet as well as bone pain. Bathing in water that is warm rather than hot and patting rather than rubbing dry may help.
Without treatment, most people who have polycythemia vera live less than 2 years. Death usually results from blockage of a crucial blood vessel. When treated, most people live at least 10 to 15 years.