Flow cytometric detection of platelet-associated immunoglobulin in patients with immune thrombocytopenic purpura and nonimmune thrombocytopenia

We increased the specificity of flow cytometric detection of platelet-associated immunoglobulin (PAIg) by a combination of platelet gating and cutoff for positivity determined by the use of receiver operating characteristic (ROC) curve analysis, and we evaluated the significance of elevated PAIg in nonimmune thrombocytopenic purpura (ITP) patients. Blood samples from 118 patients with a platelet count <100 × 10⁹/L were used in this study. Flow cytometric detection of PAIg was performed. To obtain the cutoff of the surface-bound immunoglobulin for the discrimination of ITP and non-ITP, ROC curve analysis was used. The sensitivity of a positive PAIgG and PAIgM test for ITP in thrombocytopenic patients was 74.6%; the specificity was 79.7%; the positive predictive value 78.6%; and the negative predictive value 75.8%. Among 3 patients with myelodysplastic syndrome, 2 showed increased PAIg. Six of 20 patients with benign disease showed positivity for PAIg. Among these patients, 4 with elevated PAIg were diagnosed with liver disease. This study demonstrates that flow cytometric detection of PAIg combined with ROC curve analysis is a convenient, sensitive, and specific test, compared to previous methods, and it is useful for the differential diagnosis of thrombocytopenic patients.