Classification and external resources
ICD-10 D47.3
ICD-9 289.9
DiseasesDB 27591
MedlinePlus 000543
eMedicine med/2267 ped/2238
NCI Thrombocytosis
Patient UK Thrombocytosis

Thrombocytosis (or thrombocythemia) is the presence of high platelet counts in the blood, and can be either primary (also termed essential and caused by a myeloproliferative disease) or reactive (also termed secondary). Although often symptomless (particularly when it is a secondary reaction), it can predispose to thrombosis in some patients. Thrombocytosis can be contrasted with thrombocytopenia, a loss of platelets in the blood.

In a healthy individual, a normal platelet count ranges from 150,000 and 450,000 per mm³ (or microlitre) (150–450 x 109/L).[1] These limits, however, are determined by the 2.5th lower and upper percentile, and a deviation does not necessary imply any form of disease. Nevertheless, counts over 750,000 (and especially over a million) are considered serious enough to warrant investigation and intervention.

Signs and symptoms

High platelet levels do not necessarily signal any clinical problems, and are picked up on a routine full blood count. However, it is important that a full medical history be elicited to ensure that the increased platelet count is not due to a secondary process. Often, it occurs in tandem with an inflammatory disease, as the principal stimulants of platelet production (e.g. thrombopoietin) are elevated in these clinical states as part of the acute phase reaction.

High platelet counts can occur in patients with polycythemia vera (high red blood cell counts), and is an additional risk factor for complications.

A very small segment of patients report symptoms of erythromelalgia, a burning sensation and redness of the extremities that resolves with cooling and/or aspirin use.[citation needed]

Scientific literature sometimes excludes thrombocytosis from the scope of thrombophilia by definition,[2] but practically, by the definition of thrombophilia as an increased predisposition to thrombosis,[3][4] thrombocytosis (especially primary thrombocytosis) is a potential cause of thrombophilia. Conversely, secondary thrombocytosis very rarely causes thrombotic complications.[5]


Laboratory tests might include: full blood count, liver enzymes, renal function and erythrocyte sedimentation rate.

If the cause for the high platelet count remains unclear, bone marrow biopsy is often undertaken, to differentiate whether the high platelet count is reactive or essential.


Increased platelet counts can be due to a number of disease processes:

Over-medication with drugs that treat thrombocytopenia, such as eltrombopag or romiplostim, may also result in thrombocytosis. Other causes include the following

The vast majority of causes of thrombocytosis are acquired disorders, but in a few cases, they may be congenital, such as thrombocytosis due to congenital asplenia.[7]


Often, no treatment is required or necessary for reactive thrombocytosis. In cases of reactive thrombocytosis of more than 1,000x109/L, it may be considered to administer daily low dose aspirin (such as 65 mg) to minimize the risk of stroke or thrombosis.[8]

However, in primary thrombocytosis, if platelet counts are over 750,000 or 1,000,000, and especially if there are other risk factors for thrombosis, treatment may be needed. Selective use of aspirin at low doses is thought to be protective. Extremely high platelet counts in primary thrombocytosis can be treated with hydroxyurea (a cytoreducing agent) or anagrelide (Agrylin).[9]


  1. ^ Kumar & Clark (2005). "8". Clinical Medicine (Sixth ed.). Elsevier Saunders. p. 469. ISBN 0-7020-2763-4. 
  2. ^ "Management of patients with thrombophilia". Drug and Therapeutics Bulletin 33 (1): 6–8. 1995. PMID 7587981. doi:10.1136/dtb.1995.3316.  edit [1]
  3. ^ Mitchell RS, Kumar V, Abbas AK, Fausto N (2007). "Chapter 4". Robbins Basic Pathology (Eighth ed.). Philadelphia: Saunders. ISBN 1-4160-2973-7. 
  4. ^ Heit JA (2007). "Thrombophilia: common questions on laboratory assessment and management". Hematology Am. Soc. Hematol. Educ. Program 2007 (1): 127–35. PMID 18024620. doi:10.1182/asheducation-2007.1.127. 
  5. ^ medscape > Pediatric Thrombocytopenia By Susumu Inoue. Updated: Apr 19, 2010
  6. ^
  7. ^ Chanet, V.; Tournilhac, O.; Dieu-Bellamy, V.; Boiret, N.; Spitz, P.; Baud, O.; Darcha, C.; Travade, P.; Laurichesse, H. (2000). "Isolated spleen agenesis: A rare cause of thrombocytosis mimicking essential thrombocythemia". Haematologica 85 (11): 1211–1213. PMID 11064471.  edit [2]
  8. ^ Thrombocytosis, Secondary Treatment & Management from Medscape. Author: Koyamangalath Krishnan, MD, FRCP, FACP; Chief Editor: Emmanuel C Besa, MD. Updated: Oct 4, 2009
  9. ^ Harrison, CN; Campbell PJ, Buck G, Wheatley K, East CL, Bareford D, Wilkins BS, van der Walt JD, Reilly JT, Grigg AP, Revell P, Woodcock BE, Green AR, United Kingdom Medical Research Council Primary Thrombocythemia 1 Study. (2005). "Hydroxyurea compared with anagrelide in high-risk essential thrombocythemia.". NEJM 353 (1): 33–45. PMID 16000354. doi:10.1056/NEJMoa043800.