Description, Causes and Risk Factors:

Thrombocytosis is elevation of the peripheral blood platelet count to values > 400,000/L. It is common in infancy and childhood, occurring in 3 to 13% of children. Extreme thrombocytosis is uncommon, occurring in less than 2% of the children, but may be more common in critically-ill children. While in older adults an elevated in platelet count can signify an underlying hematological disease, in children in almost every case the elevated platelet count is due to another medical condition such as acute infection, chronic inflammation, collagen vascular and renal disease, Langerhans cell histiocytosis, iron deficiency, hemolytic anemia, and Kawasaki disease.

Drugs are another less frequent cause of secondary thrombocytosis. In children, splenectomy is a surgical cause of thrombocytosis that can occasionally be extreme, but without psychological consequences, unless associated with thrombophilic factors.


    Primary Thrombocytosis: Thrombocytosis caused by an alternation in hematopoietic cells, the serum level of the thrombopoietin (TPO). The main cytokine responsible for the production of platelets is low or normal. Primary thrombocytosis can be hereditary (rare) or acquired (more frequent, in myeloproliferative neoplasms (MPN) and in myelodysplastic syndrome (MDS)). In MDS, abnormalities of chromosomes 5 or 3 are frequently found.

  • Secondary Thrombocytosis: Thrombocytosis due to an external cause; the serum level of TPO is frequently elevated. Secondary thrombocytosis is usually acquired ailments resulting in elevated platelet counts include inflammation, iron deficiency, and asplenia. In rare cases secondary thrombocytosis is hereditary.

  • Hereditary Thrombocytosis: Primary or secondary thrombocytosis due a genetic alteration that can be transmitted to offspring that is with a familial, or hereditary, genetic cause. Major progress has been made in recent years in understanding the biology of hereditary thrombocytosis. We now know that mutations in two genes, THPO and MPL, can cause hereditary thrombocytosis.

Major progress in understanding the pathogenesis in patients with thrombocytosis has been made by identifying mutations in the key regulators of thrombopoietin: the thrombopoietin receptor MPL and JAK2. Together, these mutations can be found in 50% to 60% of patients with essential thrombocythemia or primary myelofibrosis and in 10% to 20% of hereditary thrombocytosis. A decrease in expression of the MPL protein can cause thrombocytosis even in the absence of mutations in the coding sequence, due to a shift in the balance between stimulation of signaling in megakaryopoiesis and removal of thrombopoietin by receptor mediated internalization in platelets. When present in a heterozygous state the JAK2-V617F mutation preferentially stimulates megakaryopoiesis and in most cases manifests as essential thrombocythemia (ET), whereas homozygous JAK2-V617F reduces megakaryopoiesis in favor of increased erythropoiesis, resulting in polycythemia vera and/or myelofibrosis. In 30% to 40% of patients with ET or primary myelofibrosis (PMF) and in 80% to 90% of pedigrees with hereditary thrombocytosis the disease-causing gene remains unknown. Ongoing genetic and genomic screens have identified genes that, when mutated, can cause thrombocytosis in mouse models. A more complete picture of the pathways that regulate megakaryopoiesis and platelet production will be important for finding new ways of controlling platelet production in patients with thrombocytosis.


Symptoms May Include:

    Bleeding from the gastrointestinal tract, respiratory system, urinary tract, or skin.

  • Bleeding from the gums.

  • Bleeding (prolonged) from surgical procedures or tooth removal.

  • Bloody stools.

  • Dizziness.

  • Easy bruising.

  • Headache.

  • Nosebleeds (epistaxis).

  • Numbness of the hands or feet.

  • Ulcers on the fingers or toes.

  • The condition may even cause strokes in some people.


Diagnosis May Include:

    Physical Exam: A physical exam may show an enlarged spleen or liver. There may be abnormal blood flow in the toes or feet, as well as skin damage caused by that abnormal blood flow.

  • Complete blood count (CBC): This test determines the number of platelets in your blood.

  • Blood smear: A small amount of your blood is examined under a microscope to view the condition of your platelets, such as whether they're abnormally large or clumped together.

  • Genetic testing: Special tests can determine whether you have chromosomal abnormalities that can cause a high platelet count and whether you have a JAK2 gene mutation.

  • Other blood tests: Your doctor may check the level of iron in your blood or test for markers of inflammation.

Other laboratory Tests:

    Erythrocyte sedimentation rate (ESR).

  • C-reactive protein (CRP).

  • Fibrinogen level.

  • Factor VIII procoagulant activity.

  • Von Willebrand antigen level.

Imaging: Chest X-ray and abdominal ultrasound may be indicated to exclude undetected sources of infection or malignancy. Ultrasound may also be useful to assess the spleen, especially when it is not palpable. To be palpable it must be at least twice the normal size.

In more severe cases:

    Bone marrow aspiration: Your doctor extracts a small amount of your liquid bone marrow through a needle and examines it under a microscope, looking for abnormal cells.

  • Bone marrow biopsy: Your doctor takes a sample of solid bone marrow tissue through a needle for examination under a microscope. If you have ET, your bone marrow has a higher than normal number of the large cells that make platelets (megakaryocytes).


Patients who have no symptoms may remain stable and only require routine check-ups by their physician. For those with symptoms, a few treatment options are available. One is to treat the disease that is causing thrombocytosis. In some cases, the patient can take aspirin to help prevent blood clots. The low dose used for this purpose does not usually cause stomach upset or bleeding.

In essential thrombocytosis, medications such as hydroxyurea or anagrelide are used to suppress platelet production by the bone marrow. These medications usually have to be taken indefinitely. In cases of severe life-threatening thrombocytosis, a procedure called plateletpheresis is performed to immediately lower the platelet count to safer levels. In this procedure, a special instrument is used to remove blood from the patient, separate and remove the platelets, and then return the other blood cells to the patient.

NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.


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