Detection of platelet-associated immunoglobulins by flow cytometry for thediagnosis of immune thrombocytopenia: a prospective study and critical review

Background and Objectives. Flow cytometry (FC) to Identify platelet-associa ted (PA) Immunoglobulin (Ig) is a potentially useful diagnostic test for id io-pathic thrombocytopenic purpura (ITP). However, the restricted applicati on of PAIg measurement to thrombocytopenic populations primarily comprised of ITP patients will artificially enhance the test's diagnostic specificity . For this reason, we performed a prospective study in which the results of sensitive technique for detecting PAIg, as is FC, are correlated to the ca use of the thrombocytopenia Design and Methods. A total of 118 patients with let counts <100x10(9)/L an d 30 normal donors with a platelet count >200x10(9)/L were studied for PAIg ; employing a flow cytometer, Forty-two children and 20 adults were diagnos ed as having immune thrombocytopenia and 27 children and 29 Its had non-imm une thrombocytopenia of different etiologies. Results. Raised levels of PAIg were found in 56/62 patients with immune thr ombocytopenia and in 34/56 patients with non-immune thrombocytopenia. Diagn ostic values of PAIg for the detection of uno thrombocytopenia were: sensit ivity 90.3% specificity 39.3%, An enzyme-linked immunoabsorbant assay (ELIS A) for the detection of autoantibodies to platelet glycoprotein (GP) comple xes used in adults, 9 with immune-related thrombocytopenia and 16 with non- immune thrombocytopenia, in order to determine the true non-specific nature of the positive PAIg test, By ELISA, 8/9 patients with immune thrombocytop enia and 7/16 with non-immune thrombocytopenic disorders showed autoantibod ies to platelet GP complexes. Interpretation and Conclusions: PAIg detection by constitutes a sensitive b ut non-specific assay thus making it unnecessary and inappropriate for esta blishing the diagnosis of ITP. (C) 2000, Ferrata Storti Foundation.