Frequency of Seroconversion in Aquaporin-4 Antibody Testing: Insights From Real-World Data

Clinicians often repeat aquaporin-4-immunoglobulin G (AQP4-IgG) testing in case of possible seroconversion. Compared with older, less sensitive immunofluorescence assays (IFA), cell-based assays (CBA) offer higher sensitivity. This study assessed the frequency of seroconversion in a retrospective Cleveland Clinic cohort (2006-2024) of 451 patients with an initial negative AQP4-IgG result who underwent serial testing. Seroconversion occurred in 4.3% (7/170) of patients initially tested by tissue IFA, but in none (0/263) of those tested by CBA. The lack of AQP4-IgG seroconversion after a negative CBA, with only rare cases after a negative IFA, suggests that repeat AQP4-IgG testing is low yield unless prior testing used older methods such as IFA.