Differential Diagnosis of Immune Thrombocytopenia

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The differential diagnosis of immune thrombocytopenia (ITP) has evolved in recent years, explains Howard A. Liebman, MD. Revised guidelines were recently released describing that the pathway of diagnosis is based primarily on the identification of thrombocytopenia (<100,000 platelets per microliter, with and without bleeding manifestations) without other associated cytopenias. In addition, physician-reviewed blood smears should show no morphologic abnormalities of the cells that are involved, according to the new guidelines by the International Working Group in Immune Thrombocytopenia and the American Society of Hematology both published.

Despite these recent revisions, challenges remain in the diagnosis of ITP, notes Keith McCrae, MD. There are no diagnostic tests specifically for ITP; subsequently, it is often referred to as a diagnosis of exclusion. McCrae explains that several things may cause low platelet counts, including medications, infectious agents, and even viral infections.

Certain infections such as hepatitis C and HIV are strongly associated with ITP. Patients may have congenital or inherited thrombocytopenias, which are often difficult to distinguish from ITP. In these situations, the condition may not be properly diagnosed until a patient is treated for ITP and does not have a typical response to therapy.

Several strategies exist to differentiate between ITP and pseudo thrombocytopenia, notes Ivy Altomare, MD. One approach is to look at the peripheral smear and count the number of platelets and clumps of platelets.

Drug-induced thrombocytopenia can make the diagnosis of ITP more challenging, since a multitude of drugs can cause low platelets to some extent. The most common drugs are aspirin, ibuprofen, nonsteroidal anti-inflammatory drugs, and additional agents, such as some of the antiseizure medications, H2 blockers, and even simvastatin, Altomare notes. One strategy to assess drug-induced thrombocytopenia is to discontinue the suspected medication; if it is the cause, the thrombocytopenia will usually resolve within a week.

Several other conditions may lead to isolated thrombocytopenia, including complications of cirrhosis or congestive heart failure, as well as folate deficiency or alcohol-induced bone marrow toxicities. Finally, differential diagnosis may encompass additional disorders, including thrombotic thrombocytopenic purpura, heparin-induced thrombocytopenia, and disseminated intravascular coagulation.