When would you repeat antibody testing for seronegative myasthenia gravis?

I will usually recheck in 1-2 years, but I mostly focus on acetylcholine receptor antibodies. I have never seen seroconversion from MuSK negative to MuSK positive.

Also, if initial antibody testing for Acetylcholine receptor binding/modulating and MuSK antibodies is negative by RIA assay, I recommend testing them by cell-based assay. CBA for MuSK antibodies is done by several labs. CBA for AChR antibodies in the US is offered for clinical (non-research) testing only through one lab that I am awa...