What is immune thrombocytopaenic purpura? Immune Thrombocytopaenic Purpura (ITP) is a disease affecting platelets in the blood. Platelets are small cells which are needed for blood to clot normally. In ITP the body’s immune system produces antibodies which attack and destroy platelets; thrombocytopaenia means a reduced number of platelets. The normal platelet count is from 150-450 x 109 per litre of blood. ITP patients have low platelet counts but their platelets function normally; purpura means purple and describes the bruising under the skin and mucous membranes, such as the lining of the mouth, resulting from the lack of platelets. Acute ITP is usually seen in young children and often, but not always, follows a viral infection. Onset is quite abrupt. About 85% of children recover within one year and the illness never returns. Chronic ITP means a case which has lasted longer than six weeks. It may occur at any age and affects women about three times more often than men. It has a slower onset and may fluctuate in severity, that is it appears to improve and then worsen again. From http://www.doctoronline.nhs.uk/masterwebsite1Asp/targetpages/specialts/haem/itp.asp