Immune thrombocytopenia (ITP) is an autoimmune disorder characterised by isolated thrombocytopenia of variable severity (haemoglobin and white cells are expected to be normal). IgG autoantibodies directed against platelet antigens reduce platelet lifespan in the circulation. Megakaryocytes in the bone marrow and platelet production are normal to increased.
The differential diagnosis includes other causes of peripheral platelet destruction, particularly portal hypertension with Hypersplenism, Thrombotic thrombocytopenic purpura, Disseminated intravascular coagulation and sepsis; and bone marrow infiltrates.
Examination of the Blood film, INR and APTT should be performed in all cases of thrombocytopenia, particularly to exclude spurious thrombocytopenia associated with platelet clumping, red cell fragmentation of microangiopathic haemolysis and Thrombotic thrombocytopenic purpura (TTP). Imaging of the spleen should be considered to rule out hypersplenism.
INR and APTT should be performed to exclude a more complex coagulopathy.
Bone marrow biopsy is required in many but not all cases to make a diagnosis, and is normal or shows increased megakaryocytes. Platelet Ab theoretically should be the definitive diagnosis, and may be useful, but suffer from poor reproducibility. Other causes of thrombocytopenia need to be considered.
See also Thrombocytopenia.