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Thrombocytosis is a blood disorder in which the body produces a surplus of platelets (thrombocytes).


Thrombocytosis is an abnormally increased number of platelets in the blood. Platelets are blood cells that stick together, helping blood to clot. Thrombocytosis is a condition that may have many causes.
Throbocytosis is classified as one of two types. Secondary thrombocytosis can be traced to another cause, such as inflammation, severe bleeding, iron deficiency, or some cancers. Primary thrombocytosis (or essential thrombocythemia) is a single disease entity, with unique clinical characteristics.

Causes and symptoms

The cause of essential thrombocytosis is unknown.
Secondary thrombocytosis may develop as a result of:
  • acute hemorrhage or infection
  • anemia
  • arthritis and other chronic inflammations
  • cancer
  • exercise
  • iron deficiency
  • medication
  • csteoporosis
  • removal of the spleen (splenectomy)
  • polycythemia vera (a disorder affecting other red blood cells, as well as platelets)
  • stress
  • surgery


Two of every three patients who have thrombocytosis do not have any symptoms of the disease at the time of diagnosis. Younger patients may remain symptom-free for years.
Enlargement of the spleen is detected in 60% of patients with thrombocytosis. The liver may also be enlarged. As many as half of all patients experience bleeding from the skin, gums, or nose; and 20-50% have some blockage of veins or arteries.
Other symptoms of thrombocytosis include:
  • bloody stools
  • bruising
  • dizziness
  • headache
  • hemorrhage
  • prolonged bleeding after having surgery or after having a tooth pulled
  • redness or tingling of the hands and feet
  • weakness. In rare instances, the lymph nodes become enlarged
The highest platelet counts usually produce the most severe symptoms. Younger patients (especially women) may not have symptoms, even though their platelet counts are very high.


Complications of thrombocytosis include stroke, heart attack, and formation of blood clots in the arms and legs.
A doctor should be notified whenever bleeding is unexplained or prolonged or the patient develops:
  • chest or leg pain
  • confusion
  • numbness
  • weakness


The patient's symptoms suggest the presence of thrombocytosis. Blood tests confirm the diagnosis.
Bone marrow aspiration (removal of a tissue sample for microscopic examination) may also be performed.


The key to treating secondary thrombocytosis is treating the underlying condition.
Any patient who has thrombocytosis should be encouraged not to smoke.
In young people who have no symptoms, this condition can remain stable for many years. These patients should be monitored by a physician, but may not require treatment.
Treatment for patients who do have symptoms focuses on controlling bleeding, preventing the formation of blood clots, and lowering platelet levels. Treatment for secondary thrombocytosis involves treating the condition or disease responsible for excess platelet production.
In 1997, the United States Food and Drug Administration (FDA) approved the use of anagrelide HCl (Agrylin) to reduce elevated platelet counts and decrease the risk of clot formation. Some patients have benefited from the use of hydroxyurea, an anti-cancer drug.
Low doses of aspirin may prevent clotting, but can cause serious hemorrhages.
If drug therapy does not bring platelet counts down to an acceptable level as rapidly as necessary, plateletpheresis may be performed. Usually combined with drug therapy and used primarily in medical emergencies, this procedure consists of:
  • withdrawing blood from the patient's body
  • removing platelets from the blood
  • returning the platelet-depleted blood to the patient


Many patients with thrombocytosis remain free of complications for long periods. However, some patients may die as a result of blood clots or uncontrolled bleeding.


There is no known way to prevent thrombocytosis.



"Primary Thrombocythemia." The Merck Page. June 3, 1998.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.


an increase in the number of circulating platelets; it may be essential or primary (see essential thrombocythemia) or secondary to a disease process such as an infection, inflammation, neoplasm, or rheumatoid process. Called also thrombocythemia.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.


An increase in the number of platelets in the circulating blood.
Synonym(s): thrombocythemia
[thrombocyte + G. -osis, condition]
Farlex Partner Medical Dictionary © Farlex 2012


An excess of platelets. See Absolute thrombocytosis, Extreme thrombocytosis, Reactive thrombocytosis.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.


An increase in the number of platelets in the circulating blood.
Synonym(s): thrombocythemia.
[thrombocyte + G. -osis, condition]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012


An increase above normal in the number of PLATELETS (thrombocytes) in the circulating blood. The normal upper limit is about 450,000 per cubic millimetre. Thrombocytosis may be a reactive process or it may be the result of a clonal increase in the number of megakaryocytes in the bone marrow. The production of platelets from megakaryocytes requires the binding of thrombopoietin to these cells. Other (disease) processes can result in increased production of thrombopoietin. In clonal thrombocytosis, impaired binding of thrombopoietin results in an increase in free thrombopoietin and increased platelet production.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005


, thrombocythemia (throm'bō-sī-tō'sis, -sī-thēmē-ă)
An increase in the number of platelets in the circulating blood.
Synonym(s): thrombocythaemia.
[thrombocyte + G. -osis, condition]
Medical Dictionary for the Dental Professions © Farlex 2012
References in periodicals archive ?
Due to her persistently increased platelets further work-up was done to evaluate the cause of thrombocytosis JAK2 V617 mutation analysis was done, which turned out to be positive.
Platelet alterations Giant platelets 11 25 Platelet clumping 31 13 Thrombocytosis 52 36 Thrombocytopenia 9 4 (*) All conditions occurred singly or in association with other conditions
The aim of this study was to evaluate whether there is a positive correlation between thrombocytosis and the development of complications after colorectal surgery.
Dehydration, infection, thrombocytosis, and trauma have been described in the pediatric population.
Polycythemia vera (PV), idiopathic myelofibrosis (IMF), and essential thrombocytosis (ET) have been traditionally classified under the "the non CML chronic myeloproliferative neoplasms"2 because they share the features: involvement of a multipotent hematopoietic progenitor cell.6 Dominance of the transformed clone over non-transformed hematopoietic progenitor cells.7-9
In contrast, thrombocytosis can lead to falsely increased serum potassium concentrations.
Patients with a blood test showing thrombocytosis should be screened for occult cancer.
Blood cell count was within normal values, which is in accordance with cutaneous mastocytosis; in systemic mastocytosis, blood cell counts may reveal anemia, thrombocytopenia, thrombocytosis, leukocytosis, and eosinophilia.
Though their function is important, too many of these platelets can lead to a condition known as thrombocytosis. Now, new research suggests that this blood disorder may be even more dangerous than previously believed, and could be an early sign of cancer.
Around two per cent of people over 40 -- up to half a million people in the UK -- have a raised blood platelet count -- known as thrombocytosis.