Objective:

Evaluate strategies to improve sensitivity of autoantibody testing for myasthenia gravis (MG) using cell-based assays (CBAs) at our centre. 

Background:

Testing for acetylcholine receptor and muscle-specific kinase antibodies (anti-AChR and anti-MuSK) is a cornerstone of MG evaluation. Anti-AChR/MuSK fixed CBA has demonstrated higher overall sensitivity than radioimmunoassay (RIA), and is first-line testing in our laboratory. However, using multiple assays has been suggested to maximize sensitivity in persistently suspicious cases of MG, and in particular live CBA testing may detect autoantibodies that are missed by RIA or fixed CBA. Other strategies reported to improve sensitivity include repeat testing by the same methodology, and performing fixed CBA at a serum dilution of 1:5 (instead of 1:10 as per manufacturer’s instructions). We evaluated these strategies prior to potential incorporation into our diagnostic algorithm.

Design/Methods:

Quality improvement/quality assurance (QI/QA) evaluation of patients at our centre who underwent anti-AChR/MuSK fixed CBA from January 2023-January 2026.

Results:

During the 3-year evaluation period, 973 patients underwent anti-AChR/MuSK fixed CBA. Of these, 127 (13.1%) exhibited autoantibody positivity, 3 (0.3%) were indeterminable, and 843 (86.6%) were negative. Testing of 78 patients represented repeat testing after initially negative anti-AChR/MuSK fixed CBA; among these, repeat fixed CBA was positive in 4 (5%). Thirteen patients with negative anti-AChR/MuSK fixed CBA underwent send-out live CBA, of whom 4 (31%) were positive. Of all 131 anti-AChR/MuSK-positive patients identified, 123 (94%) had positivity on initial fixed CBA, 4 (3%) had positivity on repeat fixed CBA, and 4 (3%) had positivity on send-out live CBA. Among 8 samples with negativity by fixed CBA at 1:10 dilution from patients with subsequent autoantibody positivity, 4 (50%) exhibited positivity at 1:5 dilution.

Conclusions:

Repeat fixed CBA at 1:10 dilution, send-out live CBA, and fixed CBA at 1:5 dilution are all strategies that may improve sensitivity of autoantibody testing for MG at our centre.