What is the significance of low igm levels in smoldering multiple myeloma?

Depends: If you have M protein from another class of immunoglobulin, then the cells producing this M protein would crowd out the other immunoglobulin producing cells in the bone marrow leading to a lower level of what that cell would ordinarily produce. Some Multiple myeloma cases are of no medical significance but needs to be followed. Many myeloma patients are prone to bacterial infections.