Platelet antibody detection in pediatric immune thrombocytopenic purpura: evaluation of three screening methods.

Background and Objectives: Immune thrombocytopenic purpura (ITP) is a common hematologic disorder, two forms of which occur in children. The detection of circulating platelet antibodies is helpful in diagnosis.
Materials and Methods: We evaluated three different immunological methods for detecting platelet antibodies in the serum of children with ITP. These were: a solid-phase red-cell adherence test (SPRCA), an enzyme immunoassay (EIA), and an immunofluorescence test (PSIF).
Results: The sensitivity of the methods in detecting IgG antibodies ranged from 28.1 (EIA) to 39.4% (SPRCA). We also looked for IgM antibodies by PSIF, thus raising the sensitivity of this test from 32.0 to 40.0%. A combination of two tests (SPRCA and EIA) allowed us to detect 61.8% positive samples. By doing all three tests, we obtained 71.3% positive samples. Finally, we reached 73.5% by adding PSIF for IgM. We found a higher frequency of circulating antibodies in both acute and chronic ITP at onset than in clinical remission. There were a few positive sera in chronic ITP, but not in the acute form in remission.
Conclusion: The individual tests each have a relatively low sensitivity, but the combination of all three increases the diagnostic effectiveness. The finding of platelet antibodies during remission may predict evolution toward a systemic autoimmune state.