You won't get IVIG covered based just on lab results (like autoantibodies, etc.), even if you have low total IgG. There have to be immunodeficiency signs aswell or other narrowly defined clinical symptoms. There is information for which indications IVIG can be covered on a regular basis in Germany. These are listed in the leaflet which comes with the medication or even better described in the so called "fachinformation". CIDP, for example, is listed as an indication in the "fachinformation". This does not mean that IVIG are coverd in every autoimmune process or neuropathy, just in the case of CIDP. CFS and POTS are no indications. An exception would be if you can take part in a scientific study which is done, for example, by a university hospital.
If you want to use IVIG outside the regular indications, you have to fit the law speaking for "Offlabel Use". One option is that you have a severe disease that will lead to death in a short period of time and for which there is no alternative treatment available. CFS will not lead to death in a short time, so we cannot apply this for our situation.
Another possibility, which is stricter, demands that you have a severe disease, for which there is no other treament available or the available treatments have been used without success. This would apply to CFS. But in this case you need to fullfill two more conditions (which makes the rule in fact very strict): 1.) There is scientific evidence which shows the treatment is beneficial AND 2.) There is consens among experts that the medication is useful for the given situation. You need to fullfill both criteria, not just one.
Concerning 1.), there are two blinded placebo-controlled studies which show IVIG useful in CFS. There are others which show the opposite. In this case I would selectivly cite the two positive studies and not mention the studies which were negative. With some luck, I would qualify for rule 1.). The problem is, and that is why I started the thread, to argue for condition 2.), namely that there is consens among experts regarding IVIG in CFS. There are not many CFS experts, in Germany just the Charité university hospital, on an international basis some more. If I claim against my insurance company that there is consens among experts regarding IVIG in CFS, I would have to back this claim up with facts, at least mention some (internationally) experts. So far I haven't found clear statements from any of them.
This is how the law speaking is in Germany. Most likely it differs more or less in your country. That means that things that worked in another country may not work in Germany and vice versa.
It ends with this: Can I somehow prove or at least make it plausbile that there is consens among experts regarding IVIG in CFS? Otherwise I have no chance to get my IVIG covered in Germany.