Assessment of platelet antibody by flow cytometric and ELISA techniques: a comparison study

Two different methods for evaluating platelet antibody were used to study 12 normal subjects and 24 patients consisting primarily of intravenous drug users (IVDUs) who were positive for human immunodeficiency virus (HIV). Total platelet-associated immunoglobulin G (IgG) and immunoglobulin M (IgM) were measured by enzyme-lined immunosorbent assay on platelet lysate, and platelet surface-associated IgG and IgM were measured by semiquantitative flow cytometry. IgG and IgM values showed significant correlations between the two measurement methods. Mean platelet surface IgG and total IgG were 3.6 and 4.3 times greater, respectively, in IVDUs than in controls, and platelet IgM was also significantly higher in IVDUs than in controls as measured by both techniques. Although mean platelet immunoglobulin levels were higher in the IVDUs with thrombocytopenia than in IVDUs with normal platelet counts, these differences did not achieve significance. These data show that platelet IgG and IgM levels are increased in IVDU-associated HIV infection and suggest that these increases are not confined to patients manifesting thrombocytopenia. The herein described platelet surface antibody and total platelet antibody measurements appear to be equally useful in studying this patient population. Specific details for generating platelet-associated immunofluorescence units are discussed.