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Objectives: Detection of acetylcholine receptor (AChR) blocking antibodies through the use of a radiolabel has become standard procedure in most laboratories. Known drawbacks associated with radioassay, including cost of radioisotopes, hazards to laboratory professionals, and manufacture and disposal of radioactive materials, have prompted investigation into replacement assays. We describe here a high-throughput immunofluorescent flow cytometric assay designed for the detection of AChR blocking antibodies., Methods: In total, 323 serum samples were tested on both the AChR blocking radioassay and the new immunofluorescent flow cytometric assay., Results: Analysis of the results revealed a 96.9% concordance between the two assay methods., Conclusions: Our results indicate that a new immunofluorescent flow cytometric AChR blocking antibody assay is not only feasible but clinically comparable in both sensitivity (91%) and specificity (99%) compared with radioassay., (© American Society for Clinical Pathology, 2016. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Objectives: To determine the clinical utility and performance characteristics of a laboratory-adapted flow cytometric method for the detection of acetylcholine receptor (AChR) modulating antibodies in myasthenia gravis (MG)., Methods: Serum samples from 120 healthy donors and 100 patients with suspected MG were assessed for the ability to reduce surface AChR concentrations (antigenic modulation) in RD (TE671) or DB40 human muscle cell lines by flow cytometry. Reference ranges were established by receiver operating characteristic curve analysis, and results were then compared with those of the current radioimmunoassay (RIA)., Results: Flow cytometric results from the RD cell line had an interpretive threshold of 46% modulation or greater and correlated best (98% sensitivity, 99% specificity) with those of the current RIA., Conclusions: The new flow cytometric method using the RD cell platform provided higher quality clinical results, a more robust and efficient assay format, a significant cost savings, and less environmental burden., (Copyright© by the American Society for Clinical Pathology.)