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Thrombocytopeni
Classification and external resources
ICD-10 D69.6, P61.0
ICD-9 287.3, 287.4, 287.5
OMIM 188000 313900
DiseasesDB 27522
MedlinePlus 000586
MeSH D013921

Thrombocytopenia (or -paenia, or thrombopenia in short ) is the presence of relatively few platelets in blood.

Generally speaking, in humans, a normal platelet count ranges from 150,000 to 450,000 platelets per microliter of blood.[1] These limits, however, are determined by the 2.5th lower and upper percentile, and a deviation does not necessarily imply any form of disease. The number of platelets in a blood sample also decreases rather quickly with time and a low platelet count may be caused by a delay between sampling and analysis.

One common definition is a number lower than 50 x 109 platelets per litre.[2][3]

Contents

Signs and symptoms

Often, low platelet levels do not lead to clinical problems; rather, they are picked up on a routine full blood count (or CBC, complete blood count). Occasionally, there may be bruising, particularly purpura in the forearms, nosebleeds and/or bleeding gums.

It is vital that a full medical history is elicited, to ensure the low platelet count is not due to a secondary process. It is also important to ensure that the other blood cell types red blood cells, and white blood cells, are not also suppressed.

Diagnosis

Laboratory tests might include: full blood count, liver enzymes, renal function, vitamin B12 levels, folic acid levels, erythrocyte sedimentation rate, and peripheral blood smear.

If the cause for the low platelet count remains unclear, bone marrow biopsy is often undertaken, to differentiate whether the low platelet count is due to decreased production or peripheral destruction.


Thrombocytopenia in hospitalized alcoholics may be caused by splenomegaly, folate deficiency, and, most frequently, a direct toxic effect of alcohol on production, survival time, and function of platelets. Platelet count begins to rise after 2 to 5 days' abstinence from alcohol. The condition is generally benign, and clinically significant hemorrhage is rare.

Causes

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

Decreased production

Increased destruction

Medication-induced

Thrombocytopenia-inducing medications include:

  • Direct myelosuppression
  • Immunological platelet destruction
    • Drug binds Fab portion of an antibody. The classic example of this mechanism is the quinidine group of drugs. The Fc portion of the antibody molecule is not involved in the binding process.
    • Drug binds to Fc, and drug-antibody complex binds and activates platelets. Heparin induced thrombocytopenia (HIT) is the classic example of this phenomenon. In HIT, the heparin-antibody-platelet factor 4 (PF4) complex binds to Fc receptors on the surface of the platelet. Since Fc portion of the antibody is bound to the platelets, they are not available to the Fc receptors of the reticulo-endothelial cells, so therefore this system cannot destroy platelets as usual. This may explain why severe thrombocytopenia is not a common feature of HIT.
    • Abciximab induced thrombocytopenia.

More extensive lists of thrombocytopenia-inducing medications are available.[6]

Treatment

Treatment is guided by etiology and disease severity. The main concept in treating thrombocytopenia is to eliminate the underlying problem, whether that means discontinuing suspected drugs that cause thrombocytopenia, or treating underlying sepsis. Diagnosis and treatment of serious thrombocytopenia is usually directed by a hematologist.

Specific treatment plans often depend on the underlying etiology of the thrombocytopenia.

Condition Treatment
Thrombotic thrombocytopenic purpura Treatment of thrombotic thrombocytopenic purpura is a medical emergency, since the hemolytic anemia and platelet activation can lead to renal failure and changes in the level of consciousness. Treatment of TTP was revolutionized in the 1980s with the application of plasmapheresis. According to the Furlan-Tsai hypothesis[7][8], this treatment theoretically works by removing antibodies directed against the von Willebrand factor cleaving protease, ADAMTS-13. The plasmapheresis procedure also adds active ADAMTS-13 protease proteins to the patient, restoring a more physiological state of von Willebrand factor multimers. Patients with persistent antibodies against ADAMTS-13 do not always manifest TTP, and these antibodies alone are not sufficient to explain the how plasmapheresis treats TTP.
Idiopathic thrombocytopenic purpura Many cases of ITP can be left untreated, and spontaneous remission (especially in children) is not uncommon. However, counts of under 50,000 are usually monitored with regular blood tests, and those with counts of under 10,000 are usually treated, as the risk of serious spontaneous bleeding is high with a platelet count this low. Any patient experiencing severe bleeding symptoms is also usually treated. The threshold for treating ITP has decreased since the 1990s, and hematologists recognize that patients rarely spontaneously bleed with platelet counts greater than 10,000—though there are documented exceptions to this observation.

Treatments for ITP include:

Thrombopoetin analogues have been tested extensively for the treatment of ITP. These agents had previously shown promise but had been found to stimulate antibodies against endogenous thrombopoietin or lead to thrombosis.

Romiplostim (trade name Nplate, formerly AMG 531) was found to be safe and effective for the treatment of ITP in refractory patients, especially those who relapsed following splenectomy.[9][10][11]

Heparin-induced thrombocytopenia Discontinuation of heparin is critical in a case of HITT. Beyond that, however, clinicians generally treat to avoid a thrombosis, and patients started directly on warfarin after a diagnosis of HITT are at excess risk of venous limb gangrene. For this reason, patients are usually treated with a type of blood thinner called a direct thrombin inhibitor such as lepirudin or argatroban, which are approved by the U.S. Food and Drug Administration (FDA). Other blood thinners sometimes used in this setting that are not FDA-approved for treatment of HITT include bivalirudin and fondaparinux. Platelet transfusions are not a routine component of the treatment of HITT, since thrombosis, not bleeding, is the usual associated problem in this illness.
Congenital amegakaryocytic thrombocytopenia Bone Marrow/Stem Cell Transplant is the only thing that ultimately cures this genetic disease. Frequent platelet transfusions are required to keep the patient from bleeding to death until transplant is done, although this is not always the case.

Veterinary treatment

Thrombocytopenia caused by Feline Leukemia Virus and Feline immunodeficiency virus retroviral infections is treated with Lymphocyte T-Cell Immune Modulator.

References

  1. ^ "Platelet count aka thrombocyte count". Lab Tests Online UK. 2004-05-28. http://www.labtestsonline.org.uk/understanding/analytes/platelet/test.html. Retrieved 2008-05-22. 
  2. ^ Correia MC, Domingues AL, Lacerda HR, et al. (December 2008). "Platelet function and the von Willebrand factor antigen in the hepatosplenic form of schistosomiasis mansoni". Trans. R. Soc. Trop. Med. Hyg.. doi:10.1016/j.trstmh.2008.11.017. PMID 19118853. http://linkinghub.elsevier.com/retrieve/pii/S0035-9203(08)00526-9. 
  3. ^ Cheung RC, McAuley RJ, Pollard JB (May 2005). "High mortality rate in patients with advanced liver disease independent of exposure to general anesthesia". J Clin Anesth 17 (3): 172–6. doi:10.1016/j.jclinane.2004.06.016. PMID 15896582. http://linkinghub.elsevier.com/retrieve/pii/S0952-8180(05)00051-6. 
  4. ^ Scaradavou A (March 2002). "HIV-related thrombocytopenia". Blood Rev. 16 (1): 73–6. doi:10.1054/blre.2001.0188. PMID 11914001. http://linkinghub.elsevier.com/retrieve/pii/S0268960X01901882. 
  5. ^ Watson, T. D (2006). "The Annals of Pharmacotherapy, Pantoprazole-Induced Thrombocytopenia". Annals of Pharmacotherapy 40: 758. doi:10.1345/aph.1G384. PMID 16569810. http://www.theannals.com/cgi/content/abstract/40/4/758. 
  6. ^ "moon.ouhsc.edu". http://moon.ouhsc.edu/jgeorge/drug%20ITP_single04.htm+. 
  7. ^ Furlan M, Lämmle B (2001). "Aetiology and pathogenesis of thrombotic thrombocytopenic purpura and haemolytic uraemic syndrome: the role of von Willebrand factor-cleaving protease". Best Pract Res Clin Haematol 14 (2): 437–54. doi:10.1053/beha.2001.0142. PMID 11686108. 
  8. ^ Tsai H (2003). "Advances in the pathogenesis, diagnosis, and treatment of thrombotic thrombocytopenic purpura". J Am Soc Nephrol 14 (4): 1072–81. doi:10.1097/01.ASN.0000060805.04118.4C. PMID 12660343. 
  9. ^ Bussel J, Kuter D, George J, McMillan R, Aledort L, Conklin G, Lichtin A, Lyons R, Nieva J, Wasser J, Wiznitzer I, Kelly R, Chen C, Nichol J (2006). "AMG 531, a thrombopoiesis-stimulating protein, for chronic ITP". N Engl J Med 355 (16): 1672–81. doi:10.1056/NEJMoa054626. PMID 17050891. 
  10. ^ AMGEN (2008-03-12). "Press release: Amgen Statement on Successful Outcome of Romiplostim Panel Meeting". Business Wire via drugs.com. http://www.drugs.com/nda/romiplostim_080313.html. Retrieved 2008-05-22. 
  11. ^ "US FDA panel backs Amgen's Nplate against ITP". Reuters. 2008-03-12. http://www.reuters.com/article/rbssHealthcareNews/idUSWAT00911720080312. Retrieved 2008-05-22. 

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