Thrombocytopenia

Thrombocytopenia means an abnormally low number of platelets in the blood.

Platelets are small cells which are involved in blood clotting. They are quite different from the blood proteins which are missing in haemophilia, which also cause clotting problems. Platelets are made in the bone marrow from other cells called megakaryocytes.

In HIV infection, the number of platelets can be low for several reasons. Bone marrow cells may produce fewer platelets either because they are directly infected by HIV or inhibited by abnormal immune responses, such as high levels of the cytokines tumour necrosis factor alpha (TNF-alpha) or tumour growth factor beta (TGF-beta), or the development of antibodies against platelets. They may also be being removed from the blood.

Low platelet counts occur in about 20% of people with HIV, at all stages of infection. Some treatment drugs, such as AZT (zidovudine, Retrovir) and cotrimoxazole (Septrin / Bactrim), can also cause thrombocytopenia. There is also evidence that HIV-positive patients with low platelet counts have lower CD4 cell counts, higher viral loads and poor virological responses to highly active antiretroviral therapy.1

Thrombocytopenia was a common complication of HIV infection prior to the introduction of antiretroviral therapy (ART). More recently, French investigators have found that even relatively short interruptions in ART significantly raise the risk of thrombocytopenia compared to continuous treatment.2 One retrospective of cases at a New York clinic also suggests an association in patients taking antiretroviral therapy with a detectable viral load, hepatitis C and cirrhosis.3

References

  1. Miguez-Burbano MJ et al. Thrombocytopenia an independent risk factor of HIV disease progression in the HAART era. Fifteenth International AIDS Conference, Bangkok, abstract MoPeB3263, 2004
  2. Bouldouyre M-A et al. Incidence and risk factors of thrombocytopenia in patients receiving intermittent antiretroviral therapy: a substudy of the ANRS 106-Window trial. J Acquire Immune Defic Syndr 52: 531-37, 2009
  3. Marks KM et al. Risk factors for thrombocytopenia in HIV-infected persons in the era of potent antiretroviral therapy. J Acquire Immune Defic Syndr 52: 595-99, 2009
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