Abstract Details

Evaluate the analytic performances of a rapid immunodot assay (iDOT) for the identification of antibodies against AQP4 in patients with NMOSD.

NMOSD refers to an inflammatory condition of the central nervous system. IgG autoantibodies against AQP4 are pathogenic and diagnostic biomarkers for NMOSD; cell-based assays (CBAs) are the most widely used test for AQP4 antibodies detection.

Sera from centres in China, France, Italy, Korea, Spain, UK were sent coded to the coordinating centre in Italy from four patient groups (1. AQP4 antibody positive NMOSD patients 2. MOG-IgG clear positive MOGAD patients 3. Clinically definite pwMS 4. Sera difficult on any assay). iDOT kits from China were sent to Italy. All samples were recoded and shipped with kits to 8 testing centres (Austria, Brazil, India, Sri Lanka, France, China, Korea, UK). iDOTs were performed at all centres; lCBAs in Korea and UK; fCBA in China. Test sensitivity was based on positive results in group 1; specificity was based on negative results in groups 2–4.

Unblinding revealed 381 sera were tested: Group 1: 126, Group 2: 106, Group 3: 93, Group 4: 56. Kits were employed close to/after expiry date in seven centres. The median sensitivity was 84.9% (range 39.7-92.9%); median specificity was 99.2% (range 98.8-99.6%). 72% of group 1 samples were positive on all iDOTs across 7 centres with only 7 (6%) samples positive in fewer than 4/7 centres. The China team performed the assay on iDOT kits 2 months old with a sensitivity of 100% and specificity of 98.8%. The fCBA was 91.2% sensitive. lCBAs were 83.7% and 100% sensitive. All three were 100% specific.

The iDOT kit performed well despite being near the end of their shelf-life. A relatively new kit performed in-house had equal sensitivity to the best lCBA and highlights great promise for this system.