Caption =
DiseasesDB = 27591
ICD10 =
ICD9 = ICD9|289.9
MedlinePlus =
eMedicineSubj = med
eMedicineTopic = 2267
eMedicine_mult = eMedicine2|ped|2238
MeshID =

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

In humans, a normal platelet count ranges from 150,000 and 450,000 per mm³ (or microlitre) (150–450 x 109/L) (Lab Tests Online UK 2004). 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.

igns 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.


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".


Increase platelet counts can be due to a number of disease processes:
* Essential (primary)
**Essential thrombocytosis (a form of myeloproliferative disease)
**Other myeloproliferative disorders such as chronic myelogenous leukemia, polycythemia vera, myelofibrosis
* Reactive (secondary)
** Inflammation
** Surgery (which leads to an inflammatory state)
** Hyposplenism (decreased breakdown due to decreased function of the spleen)
** Hemorrhage and/or iron deficiency


Often, no treatment is required or necessary for reactive thrombocytosis.

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. Aspirin at low doses is thought to be protective, and extreme levels are treated with hydroxyurea (a cytoreducing agent). The new agent anagrelide (Agrylin) has recently been introduced for the treatment of essential thrombocytosis. However, recent studies show that anegrilide is not significantly more effective than traditionally used hydroxyurea (Harrison "et al" 2005).


* 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. "Hydroxyurea compared with anagrelide in high-risk essential thrombocythemia." N Engl J Med 2005;353:33-45. PMID 16000354.
*Cite web
title=Platelet count aka thrombocyte count
author=Lab Tests Online UK

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Look at other dictionaries:

  • thrombocytosis — noun The condition of having an abnormally high number of thrombocytes (platelets) in the bloodstream; can give a predisposition to thrombosis Syn: thrombocythemia …   Wiktionary

  • thrombocytosis — An increase in the number of platelets in the circulating blood. SYN: thrombocythemia. [thrombocyte + G. osis, condition] * * * throm·bo·cy·to·sis .thräm bə .sī tō səs n, pl to·ses tō sēz increase and esp. abnormal increase in the number of blood …   Medical dictionary

  • thrombocytosis — throm·bo·cy·to·sis …   English syllables

  • thrombocytosis — n. an increase in the number of platelets in the blood. It may occur in a variety of diseases, including chronic infections, cancers, and certain blood diseases and is likely to cause an increased tendency to form blood clots within vessels… …   The new mediacal dictionary

  • thrombocytosis — noun increase in the number of platelets in the blood which tends to cause clots to form; associated with many neoplasms and chronic infections and other diseases • Hypernyms: ↑symptom …   Useful english dictionary

  • Essential thrombocytosis — DiseaseDisorder infobox Name = Essential thrombocytosis ICD10 = ICD10|D|75|2|d|70, ICD10|D|47|3|d|37 ICD9 = ICD9|238.71 ICDO = 9962/3 Caption = OMIM = 187950 DiseasesDB = 4522 MedlinePlus = 000543 eMedicineSubj = med eMedicineTopic = 2266 MeshID …   Wikipedia

  • reactive thrombocytosis — secondary thrombocytosis thrombocytosis occurring in reaction to some other disease process such as an infection, neoplasm, inflammatory process, or rheumatoid process …   Medical dictionary

  • Тромбоцитоз (Thrombocytosis) — увеличение количества тромбоцитов в крови. Может наблюдаться при различных заболеваниях, в том числе при хронических инфекциях, злокачественных опухолях и некоторых болезнях крови; тромбоцитоз является одной из причин развития повышенной… …   Медицинские термины

  • primary thrombocytosis — essential thrombocythemia …   Medical dictionary

  • essential thrombocytosis — An increased number of thrombocytes (platelets) in the blood, without a known cause. Also called essential thrombocythemia …   English dictionary of cancer terms

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