--linked to rogue antibodies being produced in the bone marrow and being introduced into the circulatory system, not necessarily.

The type of antibodies associated with blood diseases can be class IgM, IgA, or IgG, but they are generally monocolonal in nature, which is generally only revealed with the more specific immunofixation electrophoresis (IEP) test, generally down along with a quantitative enumeration of antibodies. One can have elevated polyclonal (e.g., more "normal" antibodies that are produced to specific antigens) for a lot of different reasons, including rather standard infections--the monoclonals generally show up only when there is a disease process going on in the bone marrow in which too many of these are produced without a corresponding bodily reason. (They tend to proliferate in blood cancers, for instance.)

They should do a 24-hour urine tests to look for Bence-Jones proteins, and the IEP with immunoglobulin enumeration:

http://neuromuscular.wustl.edu/antibody/mprotein.htm

I've posted that link before, but wanted to also post this one about paraproteins not associated with blood cancers, but with more solid tumors--those are associated with antibodies not produced in the bone marrow, but by the tumors themselves:

http://neuromuscular.wustl.edu/nother/paraneo.htm