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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.


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.


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


/throm·bo·cy·to·sis/ (-si-to´sis) thrombocythemia; an increase in the number of circulating platelets.


Etymology: Gk, thrombos + kytos + osis, condition
an abnormal increase in the number of platelets in the blood. Benign thrombocytosis, or secondary thrombocytosis, is asymptomatic and usually occurs after splenectomy, inflammatory disease, hemolytic anemia, hemorrhage, or iron deficiency; as a response to exercise; after chemotherapy; in chronic myelogeneous leukemia; or in advanced carcinoma, Hodgkin's disease, or other lymphomas. Essential thrombocythemia is characterized by episodes of spontaneous bleeding alternating with thrombotic episodes. The platelets may reach levels exceeding 1,000,000/μL. Compare thrombocytopenia. See also polycythemia.


An excess of platelets. See Absolute thrombocytosis, Extreme thrombocytosis, Reactive thrombocytosis.


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


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.


increased numbers of platelets in circulating blood i.e. > 400 × 109/L


, 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]

thrombocytosis (throm´bōsītō´sis),

n unusually large numbers of platelets in the circulating blood. It may occur after surgical procedures, parturition, and injury, or with thrombocythemia.
Enlarge picture


increase in the number of platelets in the circulating blood. See also thrombocythemia.

autonomous thrombocytosis
one resulting from a myeloproliferative disorder.
reactive thrombocytosis
one occurring in association with acute hemorrhage, trauma, neoplasia, etc.
References in periodicals archive ?
Clinical relevance of thrombocytosis in primary care: A prospective cohort study of cancer incidence using English electronic medical records and cancer registry data.
According to the team, if a conservative estimate of 5 percent of people with cancer have thrombocytosis before their cancer diagnosis, then a third of this group could potentially receive their cancer diagnosis months earlier.
The paper, published in the British Journal of General Practice, calls for GPs to consider a diagnosis of cancer in patients with unexpected thrombocytosis, to increase early diagnosis which can save lives.
With a diagnosis of pulmonary infection and thrombocytosis, the patient was started on antibiotic therapy and acetylsalicylic acid as antiplatelet treatment.
Thrombocytosis after major lower extremity trauma: mechanism and possible role in free flap failure.
On D3, at early-stage of disease establishment, profound thrombocytosis in the control was observed compared to the healthy, untreated group (p [less than or equal to] 0.
High ESR levels are seen in all AOSD patients, and typically, leukocytosis, normocytic-normochromic anemia, and reactive thrombocytosis are observed.
Biological findings highlighted leukocytosis with polynucleosis, thrombocytosis, normocytic anemia, hypoalbuminemia and complex metabolic imbalance (metabolic acidosis with respiratory alkalosis), leading to the stage diagnosis of sepsis through enterocolitis in the context of a presumable Hirschsprung disease.
Investigations showed increased inflammatory markers, leukocytosis, thrombocytosis, hypercalcemia, and raised angiotensin-converting enzyme.
Thrombocytosis and anti-inflammatory properties and toxicological evaluation of Carica ppaya mature leaf concentrate in a murine model.
Laboratory evaluation may reveal leukocytosis, thrombocytosis, anemia, hepatitis, and hyperferritinemia.