What lab test came back at 213 IU/ml? Have you had other thyroid tests done, such as TSH, Free T3 and Free T4? If so, can you post the results, along with the lab's reference ranges?
Actually, it's quite common for people to get more than one autoimmune disease, but your doctor is right - there's no way to know your risk since each individual is different. I, personally, have hypothyroidism/Hashimoto's, plus pernicious anemia, which is another autoimmune in which the body does not absorb vitamin B12.
I have a son with juvenile diabetes (he's 37 and was diagnosed at age 10) and a 34 yr old daughter with lupus. Juvenile diabetes and lupus are both autoimmune also.
Do a search on multiple autoimmune syndrome. Like your doctor said, no way to know your risk. I wish you the best.