Acetylcholine receptor antibodies are seen in nearly 85% of patients with generalised myasthenia gravis (MG). Two main assays are used to detect the antibodies, ELISA or Radioimmunoassay (RIA). Between 2011 and 2014, the assays in our lab were done using the ELISA technique. This study looked into the samples tested during this period to identify any false positive rates. For the purpose of the study, false positive was defined as lack of response to autoimmune myasthenia treatments (and the absence of other clinical or neurophysiological features of MG), or tests requested in error when there was no clinical suspicion of myasthenia.
696 samples were tested for AChR from 582 patients. 280 patients (48.1%) were reported to have positive AChR antibodies. 27 of these were considered to be false positive. We analysed the clinical details of these patients and have identified factors like other autoimmune diseases or malignancies to influence the test results. Since 2014, we no longer use the ELISA but the more specific RIA for testing AChR antibodies, and have not had a false positive result, yet as far as we are aware.
We recommend the use of RIA for testing AChR antibodies, and advise that clinical suspicion should always over rule any laboratory results.