When I visited my Rheumatologist this week he tested for IgG, IgA & IgM antibodies. Sure enough IgM antibodies were below normal. This finding is consistent with prior Rituximab treatment. I found the following study related to immunoglobulin testing.
Thought many of you might find this interesting:

https://bmcmusculoskeletdisord.biome...71-2474-15-178