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

## TL;DR

The study finds that seroconversion to AQP4-IgG is rare after initial negative testing, especially with modern cell-based assays.

## Contribution

The study provides real-world data on the low yield of repeat AQP4-IgG testing after initial negative results using modern assays.

## Key findings

- Seroconversion occurred in 4.3% of patients initially tested with tissue IFA.
- No seroconversion was observed in patients initially tested with cell-based assays (CBA).
- Repeat testing is low yield unless prior testing used older methods like IFA.

## Abstract

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.