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Diagnosis of idiopathic (autoimmune) thrombocytopenia purpura
Diagnosis of immune thrombocytopenia associated with systemic lupus erythematosus or other disorders associated with autoimmune phenomena
Platelet antibodies may be allo- or autoantibodies and may be directed to a wide range of antigenic "targets" on platelet cytoplasmic membranes. Alloantibodies are involved in clinical conditions such as platelet refractoriness, neonatal alloimmune thrombocytopenia, and posttransfusion purpura. In contrast, platelet autoantibodies are involved in idiopathic (autoimmune) thrombocytopenic purpura, the thrombocytopenia associated with systemic lupus erythematosus, and with the thrombocytopenia associated with sepsis (usually bacterial, occasionally fungal). Sometimes platelet autoantibodies can be detected in the patient's serum, but extensive data demonstrate that direct detection of immunologically bound immunoglobulin (usually IgG) is considerably more sensitive for autoantibody detection. The method consists of an elution step followed by solid-phase enzyme-linked immunoassay, which not only concentrates the cell-bound antibodies, but identifies the target glycoproteins against which they are directed. In most studies of autoimmune thrombocytopenia, the majority (approximately 80%) of detected autoantibodies were directed to the platelet glycoprotein IIb/IIIa and, more rarely, to other glycoproteins such as Ib/IX (approximately 11%) or Ia/IIa.
An interpretive report will be provided.
A positive test, particularly to GP IIB/IIIa or Ib/IX, in the presence of thrombocytopenia (not explained by other findings) is consistent with idiopathic (autoimmune) thrombocytopenic purpura.
Similarly, a positive test in a thrombocytopenic patient with systemic lupus erythematosus is consistent with an autoimmune cause.
Patients who are septic may also have a positive test with reactivity against most glycoproteins.
Presence of reactivity to some glycoproteins has no clearly established clinical significance.
Results of this test should be interpreted in light of the clinical circumstances.
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