Term | Definition |
ITP | An acquired thrombocytopenia caused by autoantibody-mediated destruction of platelets; the autoantibodies may also affect megakaryocytes and impair platelet production. ITP is a diagnosis of exclusion; the diagnosis cannot be made without investigations for other possible causes of thrombocytopenia. |
Bleeding severity | Several terms are used to describe bleeding severity. These are generally qualitative, and clinical judgment is needed to make these assessments.
Patients may have serious bleeding with more modest thrombocytopenia (platelet counts ≥20,000/microL), but in these cases it is important to identify another cause such as trauma or an anatomical lesion. |
Primary versus secondary ITP | Primary ITP is ITP not triggered by an apparent associated condition. Secondary ITP is ITP associated with a predisposing condition (examples listed below).* By convention, the associated condition is noted in parentheses, as in "Secondary ITP (SLE-associated)." |
Drug-induced ITP (DITP) | DITP is a drug reaction due to drug-dependent antibodies that cause platelet destruction. This syndrome should be distinguished from other, non-immune mechanisms of drug-induced thrombocytopenia such as bone marrow suppression.¶ |
New, persistent, and chronic ITP | The time elapsed since diagnosis determines whether ITP is referred to as newly diagnosed, persistent, or chronic. We use the following definitions:
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First-line versus second-line therapy | First-line generally refers to glucocorticoids, IVIG, and anti-D immune globulin; these therapies are typically used for initial treatment of newly diagnosed patients or those with recurrent thrombocytopenia following a response. Second-line generally refers to treatment for ITP that does not respond to first-line therapy, relapses after first-line therapy is tapered, or relapses frequently. Second-line treatments include splenectomy, rituximab, and TPO-RAs. |
Complete response versus partial response | A response to therapy is defined as at least doubling of the baseline platelet count and a platelet count >30,000/microL. A complete response is defined as a platelet count ≥100,000/microL; a partial response refers to a platelet count that doubles and is between 30,000 and 100,000/microL. |
Relapse | A fall in platelet count below 30,000/microL following a partial or complete response. |
Refractory disease | Definitions vary and include disease requiring treatment that persists or recurs after splenectomy or for which splenectomy is not an option. |
ITP: immune thrombocytopenia; IVIG: intravenous immune globulin; DITP: drug-induced ITP; TPO-RA: thrombopoietin receptor agonist; pRBCs: packed red blood cells.
* Examples of associated conditions include:¶ A separate table listing drugs associated with DITP is provided in UpToDate.
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