title: Comparison of the direct platelet immunofluorescence test (direct PIFT) with a modified direct monoclonal antibody-specific immobilization of platelet antigens (direct MAIPA) in detection of platelet-associated IgG.
abstract: Glycoprotein (GP)-specific platelet-associated IgG (PA-IgG) may be demonstrable in autoimmune-mediated thrombocytopenia. We studied 159 consecutive patients with histories of thrombocytopenia by a modified direct monoclonal antibody-specific immobilization of platelet antigens (direct MAIPA) assay, which immobilizes GP IIb/ IIIa, GP Ib/IX and GP Ia/IIa simultaneously. This modification requires smaller quantities of platelets than standard measurements performed separately. PA-IgG was present in 84/159 (53%) patients, as shown by the direct platelet immunofluorescence test (PIFT) with flow cytometry as a reference. PA-IgG against GP IIb/IIIa and/or GP Ib/IX and/or GP Ia/IIa was noted in 46 patients (29%), of whom 93% (43/46)-were also PA-IgG positive. The amount of PA-IgG detected by PIFT correlated directly with that detected by direct MAIPA (r = 0.71; P < 0.001). Only three patients 12548 with negative direct PIFT had GP-specific PA-IgG. GPV-specific PA-IgG was detected in 13 (10%) of the 125 patients, in whom further studies could be performed. In the subgroup of patients with GP-specific PA-IgG, the median fluorescence intensities of direct PIFT were higher than in patients with no GP-specific PA-IgG (P < 0.001). Direct PIFT and direct MAIPA divided the patients into asymmetric subgroups. However, the relative roles of these tests in the diagnosis of autoimmune-mediated thrombocytopenia await further studies.
authors.affiliation: Finnish Red Cross Blood Transfusion Service, Helsinki, Finland.
authors.forename: L
authors.initials: L
authors.lastname: Joutsi
authors.forename: R
authors.initials: R
authors.lastname: Kekomäki
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000911:Antibodies, Monoclonal / Q000032:analysis; D016824:Antigens, Human Platelet / Q000032:analysis*; D001323:Autoantibodies / Q000032:analysis; D002648:Child; D002675:Child, Preschool; D005260:Female; D019085:Fluorescent Antibody Technique, Direct; D006801:Humans; D007074:Immunoglobulin G / Q000032:analysis*; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000032:analysis; D013921:Thrombocytopenia / Q000175:diagnosis*
chemical_list: D000911:Antibodies, Monoclonal; D016824:Antigens, Human Platelet; D001323:Autoantibodies; D007074:Immunoglobulin G; D019039:Platelet Glycoprotein GPIIb-IIIa Complex