Characterization of Platelet-Associated Immunoglobulin by Flow Cytometry

Measurement of platelet-associated imunoglobulin (PAIg) has frequently been applied for the diagnosis of idiopathic thrombocytopenic purpura (ITP) and other immune thrombocytopenias. In the present study, a flow cytometry (FCM) analysis has been used to detect and characterize PAIg in 47 patients with ITP and Evans' syndrome, 13 patients with non-immune thrombocytopenia, 10 patients with autoimmune hemolytic anemia (AIHA) whose platelet counts were in normal range, and 31 healthy volunteers. With FCM measurement, mean fluorescence intensity (MFI) of platelets from patients with ITP and Evans' syndrome (2.26 +/- 2.29) was significantly higher than those from non-immune thrombocytopenia (0.33 +/- 0.39), AIHA (0.17 +/- 0.07) and control subjects (0.25 +/- 0.15) (P < 0.01). Meanwhile, the percentage of positive platelets of patients with ITP and Evans' syndrome [(44.1 +/- 29.0)%] was also higher than those of non-immune thrombocytopenia [(17.5 +/- 9.4)%], AIHA [(10.7 +/- 7.5)%] and control subjects [(16.6 +/- 8.4)%] (P < 0.01). In addition, some peak shape abnormality appeared (double peaks and peak tail) in the histogram of fluorescence intensity (log) of 11 patients (23.4%) with ITP and Evans' syndrome either alone or accompanied with quantitative alteration of MFI and/or positive platelet percentage. In seven cases, the peak shape abnormality was the unique characteristic that could be detected and have never been seen in normal platelets. This phenotypic alteration perhaps reflects the existence of different platelet populations and could be of diagnostic value. Totally, the positive result of FCM measurement in patients with ITP and Evans' syndrome was 87.2%, slightly higher than 83.0% positive rate with ELISA method, without statistical difference. The correspondent rate of the results of these two analytical settings was 85.1%. This study shows that FCM assay is a rapid and sensitive method for the measurement of PAIg and seems to be suitable as a novel routine diagnostic technique of immune thrombocytopenia.