Our normal blood has red blood cells, which carry oxygen and nutrients to the organs of the body, as well as white blood cells, which among their many roles fight infection. Blood also is composed of platelets; cells which help to keep the blood clotting mechanism in order. While too few platelets can cause abnormal bleeding disorders, too many platelets can also cause problems in the body. This condition is called thrombocytosis.

In thrombocytosis (also sometimes called thrombocythemia), an excess of platelets is produced, leading to the abnormal blood clotting. Platelets are produced in the bone marrow by cells called megakaryocytes. Megakaryocytes in these disorders become abnormal and produce too many platelets.

The usual age of presentation of thrombocytosis is after the age of 50 (commonest between ages 50 and 60) and occurs slightly more in women than men. It is called primary when the cause isn't known and secondary when the cause is another condition, such as bleeding, infection, cancer, rheumatoid arthritis, or a removal of the spleen, among other causes.

The most common clinical problem is thrombosis. This risk of thrombosis (the formation of clots that appear in the blood system) rises with age. A blood clot that obstructs a major vein in the circulatory system can have serious consequences.

Before treatment, a doctor first looks to rule out a secondary cause of this disorder. If it is not primary disease, platelet counts usually reduce once the causative disease is treated. If no cause for the increased platelet count is found (indicating primary disease), medication that slows platelet production is generally administered. Treatment is not usually started until the platelet count rises over 750,000 per microliter. Hydroxyurea, anagrelide and even interferon are drugs that are effective, and they are given until the platelet count falls below 600,000. If drugs are not effective, an exchange process called plasmaphoresis may be used, where blood is taken out, platelets are removed, and the blood reinfused back into the affected patient.

In and of itself, thrombocythemia/thrombocytosis are rather indolent disorders that do allow long-term survival. Average survival may be longer than 15 years from time of diagnosis. One major problem is thrombosis - when a blood clot breaks off and lodges in a body organ where significant damage can be done from the interruption of blood flow to that organ. A second problem is a slow progression to leukemia - there is a 5% risk of transformation to leukemia over 15-20 years.

The information contained on this page is not intended to provide medical advice, which should be obtained directly from your physician.