Hello – TSI antibodies are the antibodies that cause the thyroid to overproduce thyroid hormone in Graves’ disease. But even if you don’t have any thyroid function due to RAI or thyroidectomy, these antibodies can still have an effect on the eyes.
The use of “normal” in regards to antibody tests is a bit of a misnomer. A person without Graves’ will have zero antibodies. However, the cutoff is set somewhat higher for diagnostic reasons to make certain that people above the cutoff definitely have Graves’ disease.
Some doctors use TSI to monitor the course of thyroid eye disease, believing that surgery should not be done until TSI has dropped below the cutoff. Other eye doctors will rely more on symptoms than on TSI testing.
Hope this helps!