OBJECTIVETo establish a method for detecting platelet-associate autoantibodies against platelet-specific receptors using cytometric bead array, and compare the clinical usefulness of this method and modified indirect monoclonal antibody immobilization of platelet antigen technique (MAIPA) in the differential diagnosis of idiopathic thrombocytopenic purpura (ITP) from non-immune thrombocytopenic purpura (non-ITP).

METHODSThe microbeads were coated with monoclonal antibodies against glycoprotein IIb/IIIa (CD41a), platelets were isolated from blood samples, then platelet lysate was incubated with the coated microbeads, and R-Phycoerythrin-conjugated goat-antihuman IgG polyclonal antibodies, finally analyzed with flow cytometry. GP IIb/IIIa autoantibodies in sample plasma were measured by modified indirect MAIPA at the same time.

RESULTSThe individual fluorescence level was calculated as the ratio to the three controls. The mean ratios were 3.36 (range 0.84 - 22.94) in the ITP group, 1.16 (range 0.67 - 5.59) in the non-ITP patient and 1.08 (range 0.72 - 1.76) in the healthy controls. There was a highly significant difference (P <0.01) between the ITP patients and either the non-ITP patients or the normal controls. If the up limit of healthy controls was set as cutoff value, ratio of greater than 1.76 was considered positive. Cytometric bead array had a sensitivity of 71.43%, a specificity of 94.28% and a positive predictive value of 95.24% for the diagnosis of ITP, the sensitivity being higher than that of modified indirect MAIPA' s (5179%) (chi2 = 4.57, P <0.05). The ROC curve showed the discriminative validity of cytometric bead array was 0.916.

CONCLUSIONFlow cytometric bead method for detection of platelet-associate autoantibodies against platelet-specific receptors is a more rapid, better reproducibility and higher sensitivity than modified MAIPA, and has a potential value in promoting the diagnosis of ITP and guiding treatment.