If your total is 20 then it is present in your blood. Most people without MG don’t have it present in their blood. The following came from a lab test site:

AChR antibodies are not normally present in the blood. They are autoantibodies and their presence indicates an autoimmune response. If a person has AChR antibodies and symptoms of myasthenia gravis (MG), then it is likely that the person has this condition.

I hope this helps.

Jim