Rheumatoid Arthritis, Lupus, Sjogrens Syndrome & Multiple Sclerosis are just a few of the many autoimmune diseases. When someone is afflicted with an autoimmune disease, their immune system has become dysfunctional and begun attacking tissues or organs in the body. Some doctors theorize that fybromyalgia and ME/CFS are precursors to autoimmune disease, but there is no consensus on this idea. While others have considered that ME/CFS & Fibromyalgia are already autoimmune diseases.
At this time, Fybromyalgia and ME/CFS are not classified as autoimmune diseases although they share many of the same symptoms. A doctor can do blood tests to find most autoimmune diseases. When those tests come back negative, diagnoses of ME/CFS or Fybromyalgia are considered.
Anti Nuclear Antibody Test
An ANA (Anti-nuclear Antibody) titer is usually done with the other autoimmune blood tests. Anything higher than 1:40 is considered indicative of autoimmune disease. In my personal case, I have had several positive ANA titers but no blood test results that indicate any particular autoimmune disease. One doctor I saw gave me a diagnosis of "Fybromyalgia with positive ANA" but I have no idea what that means.
Basically, if you don't have a positive blood test result for an autoimmune disease, it seems, that without really knowing what is wrong with you, a doctor will probably give you a Fibromyalgia and/or ME/CFS diagnosis, depending on your symptoms. This has been my experience and others I've spoken to. I have seen five doctors so far and am getting ready to see my sixth.