A prospective comparison of four techniques for measuring platelet‐associated IgG
Journal Articles
Overview
Research
Identity
Additional Document Info
View All
Overview
abstract
SummaryWe describe a prospective study comparing four different assays for PAIgG. Platelets from patients with a variety of thrombocytopenic disorders were collected into ACD, washed, and the PAIgG then measured using three assays for surface PAIgG. These included: (a) a direct binding assay using 125I‐monoclonal anti‐IgG (MoAb); (b) a direct binding assay using 125I‐staphylococcal protein A (SPA); and (c) a two‐stage assay. PAIgG also was measured using an assay for ‘total’ PAIgG following platelet lysis. The mean ± SD number of molecules of IgG per platelet on washed platelets from 29 healthy, non‐thrombocytopenic controls was: 86 ± 80 (125I‐MoAb); 94 ± 96 (125I‐SPA); 3520 ± 1890 (two‐stage surface assay); and 10 850 ± 3720 (total PAIgG). A total of 62 different patients with idiopathic thrombocytopenic purpura or thrombocytopenia complicating systematic lupus erythematosus, and 73 different patients with‘non‐immune’ thrombocytopenia, were tested using each of the four assays. These ‘non‐immune’ thrombocytopenic patients included patients with carcinoma, septicaemia, pre‐eclampsia, chronic leukaemia, thrombotic thrombocytopenic purpura, haemolytic uraemic syndrome, acute leukaemia and myelodysplasia. All four essays gave similar results for both the immune and non‐immune thrombocytopenic patients. The sensitivity of the assays for the most severely thrombocytopenic patients with immune thrombocytopenia was: MoAb 60%; SPA 88%; two‐stage 82%; and‘total’ PAIgG 88%. The specificity of the four assays in the non‐immune thrombocytopenic patients was 57%‘total’ PAIgG; 63% two‐stage surface; 25% SPA; 38% MoAb. There was no quantitative cut‐off point that could be used to segregate the non‐immune thrombocytopenic patients from the immune thrombocytopenic patients. These results indicate that all of these assays share a similar high sensitivity but low specificity for ITP.
