Idiopathic Thrombocytopenic Purpura - Diagnosis

Diagnosis

The diagnosis of ITP is a process of exclusion. First, the clinician has to determine that there are no blood abnormalities other than low platelet count, and no physical signs except for signs of bleeding. Then, the secondary causes (usually 5–10 percent of suspected ITP cases) should be excluded. Secondary causes could be leukemia, medications (e.g., quinine, heparin), lupus erythematosus, cirrhosis, HIV, hepatitis C, congenital causes, antiphospholipid syndrome, von Willebrand factor deficiency, onyalai and others. In approximately one percent of cases, autoimmune hemolytic anemia and ITP coexist, a condition referred to as Evans syndrome.

Despite the destruction of platelets by splenic macrophages, the spleen is normally not enlarged. In fact, an enlarged spleen should lead a clinician to investigate other possible causes for the thrombocytopenia. Bleeding time is usually prolonged in ITP patients. However, the use of bleeding time in diagnosis is discouraged by the American Society of Hematology practice guidelines. A normal bleeding time does not exclude a platelet disorder.

A bone marrow examination may be performed on patients over the age of 60 and those who do not respond to treatment, or when the diagnosis is in doubt. On examination of the bone marrow, an increase in the production of megakaryocytes may be observed and may help in establishing a diagnosis of ITP. An analysis for anti-platelet antibodies is a matter of clinician's preference, as there is disagreement on whether the 80 percent specificity of this test is sufficient.