What are the key diagnostic criteria for immune thrombocytopenia (ITP) in adults?

The key diagnostic criteria for immune thrombocytopenia (ITP) in adults include isolated thrombocytopenia with a platelet count typically below 100 x 10⁹/L, in the absence of other causes of thrombocytopenia. Diagnosis is primarily clinical and by exclusion, requiring a thorough history, physical examination, and laboratory tests to rule out secondary causes such as infections, medications, or other hematological disorders ¹.

There is no definitive diagnostic test for ITP; instead, diagnosis relies on:

• Persistent isolated thrombocytopenia without anemia or leukopenia.
• Exclusion of other causes of thrombocytopenia, including bone marrow disorders, liver disease, or systemic illnesses.
• Peripheral blood smear showing reduced platelets but otherwise normal morphology.
• Bone marrow examination is not routinely required but may be considered in atypical cases or if diagnosis is uncertain.

Additional supportive features include the absence of splenomegaly and normal coagulation studies. The presence of bleeding symptoms varies and is not required for diagnosis ¹.

Recent literature emphasizes that ITP remains a diagnosis of exclusion and highlights the importance of ruling out secondary causes and mimics through detailed clinical and laboratory evaluation (Lambert and Gernsheimer, 2017; Neunert et al., 2019; Neunert et al., 2024).