Idiopathic thrombocytopenic purpura laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Laboratory Findings
- The diagnosis of ITP is a diagnosis of exclusion.
- Check there are no other blood abnormalities except for decrease platelet count and no physical signs except for signs of bleeding.
- Then the secondary causes ( 5-10% of ITP cases).
- Secondary causes could be leukemia, medications (e.g. quinine, heparin), lupus erythematosus, cirrhosis, HIV, hepatitis C, congenital causes, antiphospholipid syndrome, von Willebrand factor deficiency and others.
- Despite the destruction of platelets by splenic macrophages, the spleen is normally not enlarged. In fact, an enlarged spleen should lead to investigate other possible causes for the thrombocytopenia.
- Bleeding time is prolonged in ITP patients; however, the use of bleeding time in diagnosis is not recommended by the American Society of Hematology practice guidelines[1] .
- The bleeding time may or may not be prolonged in congenital or acquired platelet dysfunction, and therefore a normal bleeding time does not exclude these conditions."[2]
- Platelet-associated antibody (IgG), which was the standard test in past , is now not considered mandatory to diagnose ITP. Test for platelet antibody are not helpful as both their sensitivity and specificity are limited. The blood analysis for the antiplatelet antibodies is prefered , as there is a disagreement whether the 80% specificity of this test is sufficient. In conditions associated with bone marrow failure (aplastic anemia) thrombopoietin (TPO) levels are high whereas in ITP thrombopoietin levels are low. Thus TPO could distinguish between decreased platelets due to bone marrow failure or increased due to their destruction. The bone marrow in ITP contains normal or high numbers of megakaryocytes but they may be small or immature (& may have been damaged by antibodies).[3]
References
- ↑ "Diagnosis and treatment of idiopathic thrombocytopenic purpura: recommendations of the American Society of Hematology. The American Society of Hematology ITP Practice Guideline Panel". Ann. Intern. Med. 126 (4): 319–26. 1997. PMID 9036806.
- ↑ Liesner RJ, Machin SJ (1997). "ABC of clinical haematology. Platelet disorders". BMJ. 314 (7083): 809–12. PMID 9081003.
- ↑ Ostertag EM, Bdeir K, Kacir S, Thiboutot M, Gulendran G, Yunk L, Hayes VM, Motto DG, Poncz M, Zheng XL, Cines DB, Siegel DL (July 2016). "ADAMTS13 autoantibodies cloned from patients with acquired thrombotic thrombocytopenic purpura: 2. Pathogenicity in an animal model". Transfusion. 56 (7): 1775–85. doi:10.1111/trf.13583. PMC 4938757. PMID 27040023.