Is there a utility in getting repeat antibody testing on GBS patients after PLEX?

No, there is not, for a couple of reasons:

1. Most patients with the most common variant of GBS (AIDP) are negative for ganglioside antibodies or other antibodies against nodal/paranodal proteins. Ganglioside antibodies are more often positive in GBS variants like AMAN, AMSAN, Miller Fisher syndrome, sensory ataxic variants of GBS, etc.
2. Most importantly, there is no evidence that any second-line treatment after PLEX is effective in GBS. IVIG after PLEX was not effective based on a randomized controlled trial (PMID 9014908) and a second course of PLEX is occasionally administered empirically by some practitioners in patients who do not respond to or relapse after the first course, but again without adequate scientific evidence supporting this a...