Determination of platelet-bound glycoprotein-specific autoantibodies by flow cytometric immunobead assay in primary immune thrombocytopenia.

Objectives: Primary immune thrombocytopenia (ITP) is an autoimmune disorder characterized by premature platelet destruction induced by autoantibodies directed against platelet glycoproteins (GPs). Despite being a clinically important disorder, ITP lacks a feasible diagnostic assay for routine clinical use. This study was meant to evaluate a newly developed flow cytometric immunobead assay for determination of platelet-bound GP-specific autoantibodies in comparison with indirect monoclonal antibody-specific immobilization of platelet antigen (MAIPA) in the diagnosis of ITP.

Methods: Platelet-bound and plasma GPIIb/IIIa and GPIb/IX autoantibodies were determined by flow cytometric immunobead assay and indirect modified MAIPA, respectively. The average fluorescence level for platelet-bound, GP-specific autoantibodies was given as a ratio to three normal controls tested simultaneously.

Results: The median value of platelet-bound GPIIb/IIIa and GPIb/IX autoantibodies in ITP group were 3.09 (range 0.78, 30.2) and 3.09 (range 0.72, 19.2), respectively, which were significantly higher than non-ITP group [1.01 (0.67, 5.59) and 1.01 (0.79, 5.56), respectively, P<0.001] and normal controls [1.02 (0.72, 1.76) and 1.03 (0.79, 1.73), respectively, P<0.001]. The receiver-operating characteristics curve analysis showed an area under the curve of 0.895 for GPIIb/IIIa autoantibody and 0.859 for GPIb/IX autoantibody, respectively. Combined detection of GPIIb/IIIa or GPIb/IX autoantibodies by flow cytometric immunobead assay showed a sensitivity of 82.11% for ITP diagnosis.

Conclusion: This study demonstrated that determination of platelet-bound, GP-specific autoantibodies by flow cytometric immunobead assay was a convenient, sensitive, and specific test for the differential diagnosis of thrombocytopenic patients.