Quantification of platelet-associated IgG for differential diagnosis of patients with thrombocytopenia

Immune thrombocytopenia is due to platelet destruction by circulating glyco protein-specific antibodies and is found in various disorders. Methods for the detection of platelet-associated IgG (PAIgG) are generally sensitive bu t unspecific, whereas glycoprotein-specific assays are highly specific but less sensitive. Usefully, a sensitive screening method for PAIgG detection would also provide information for differential diagnosis. We developed a q uantitative direct Platelet Immunofluorescence Test (PIFT) by flow cytometr y and studied 79 thrombocytopenic patients with immune thrombocytopenia and other disorders. The sensitivity of the assay was 94%, its specificity 66% for the detection of a clinically obvious immune thrombocytopenia. PAIgG l evels of patients with immune thrombocytopenia differed significantly from those of other patients with low platelet counts (p <0.001). The quantitati ve PIFT proved to be a sensitive method for PAIgG detection and should ther efore be used as a screening method. In addition, it could be helpful for d ifferential diagnosis in marked thrombocytopenia where a MAIPA is not feasi ble.