From the Guidelines
ITP testing should start with a complete blood count (CBC) and peripheral smear examination, followed by a thorough medical history and physical examination to rule out other causes of thrombocytopenia. This approach is supported by the international consensus report on the investigation and management of primary immune thrombocytopenia 1. The CBC and peripheral smear examination are essential for detecting thrombocytopenia and evaluating the morphology of platelets.
When thrombocytopenia is detected (platelet count <100,000/μL), the peripheral smear should show normal-appearing platelets that are reduced in number, with otherwise normal red and white blood cells. Additional testing should include liver function tests, HIV, hepatitis C screening, and consideration of bone marrow examination in patients over 60 or those with atypical features, as recommended by the American Society of Hematology 2011 evidence-based practice guideline for immune thrombocytopenia 1.
Some key points to consider in the diagnostic approach include:
- A presumptive diagnosis of ITP is made when the history, physical examination, complete blood count, and examination of the peripheral blood smear do not suggest other etiologies for the thrombocytopenia 1.
- No single laboratory test can definitively diagnose ITP; it remains a diagnosis of exclusion.
- The presence of antiphospholipid antibodies, antinuclear antibodies, or antithyroid antibodies may be relevant in certain cases, but routine testing is not recommended in the absence of symptoms or specific risk factors 1.
- The response to ITP-specific therapy, such as intravenous immunoglobulin (IVIg) or intravenous anti-D, can be supportive of the diagnosis, but a response does not exclude secondary ITP 1.
Early and accurate diagnosis through appropriate testing allows for timely management decisions, whether observation for mild cases or treatment with corticosteroids, IVIG, or thrombopoietin receptor agonists for more severe presentations. It is essential to consider the potential causes of secondary ITP, such as antiphospholipid syndrome, autoimmune thrombocytopenia, or infection with cytomegalovirus, Helicobacter pylori, hepatitis C, or human immunodeficiency virus 1.
From the Research
ITP Testing Overview
- Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder characterized by a platelet count less than 100 × 10^9/L without anemia or leukopenia 2.
- The diagnosis of ITP requires excluding secondary causes of thrombocytopenia, and the bare minimum workup for ITP includes a complete blood count and a peripheral blood smear 2.
Diagnostic Considerations
- The diagnosis of ITP is based principally on the exclusion of other causes of isolated thrombocytopenia using patient history, physical examination, blood count, and evaluation of the peripheral blood film 3.
- The peripheral blood smear should show a small number of large platelets with normal morphology, and there should not be an increased number of schistocytes 2.
Testing for Secondary ITP
- ITP can be classified as primary (known also as idiopathic thrombocytopenic purpura) or as secondary to an underlying condition such as a malignant or nonmalignant disorder 4.
- Commonly occurring conditions associated with secondary ITP include lymphoproliferative disorders, autoimmune collagen vascular diseases, and chronic infections 4.
- Evaluation of antiplatelet antibodies, using an antigen-specific assay, was useful in supporting the diagnosis of ITP in patients with chronic HCV infection 5.