PROSPECTIVE EVALUATION OF THE CLINICAL USEFULNESS OF AN ANTIGEN-SPECIFIC ASSAY (MAIPA) IN IDIOPATHIC THROMBOCYTOPENIC PURPURA AND OTHER IMMUNE THROMBOCYTOPENIAS

The diagnosis of idiopathic immune thrombocytopenia remains a clinical diagnosis based on the exclusion of other causes of immune and nonimm une thrombocytopenia. Measurement of platelet-associated lg (PAIg), wh ile sensitive, is nonspecific for the diagnosis of immune thrombocytop enia, Published experience of antigen capture assays (including monocl onal antibody immobilization of platelet antigens or MAIPA) suggest a high sensitivity and specificity (70% to 80%) in selected groups of pa tients, In a prospective evaluation of 158 patients with thrombocytope nia from all causes, we report a sensitivity of 51% and specificity of 80% for direct MAIPA assays. MAIPA was considerably better in discrim inating immune from nonimmune thrombocytopenia than two assays of PAIg G, Antiplatelet antibodies detected by MAIPA were more frequently dire cted against the glycoprotein (GP) Ilb/llla than the GP Ib/lX complex. Our experience suggests that W1AIPA assays are useful in the laborato ry assessment of thrombocytopenia, should be performed before therapy, and that some patients with 'nonimmune' thrombocytopenia may have gen uine antiplatelet antibodies. (C) 1996 by The American Society of Hema tology.