If your IgG is low (or on the low side), then you NEED to be tested for IgG subclasses. It is VERY common to have a normal total IgG level, yet be deficient in one more of the subclasses. I'm deficient in 3 of the 4 subclasses, yet my total is just over the normal level because the first subclass (1) is the largest and I have a normal level in this category...bringing my total into a normal level.

Like I said, it is quite common for those with autoimmune disease to be immune deficient. Hopefully your hematologist will order IgG subclasses, but f not, ask him to do so.