TSI (IgG antibodies) are diagnostic of Graves’ disease. 70-100% of Graves’ disease patients have these antibodies. Generally, if they are present and you are hyperthyroid, you have Graves’ because they make the thyroid produce excessive hormones and are specific to the thyroid stimulating hormone receptor. Sometimes TSI may also appear in Hashimoto’s thyroiditis but their level is low.
Other thyroid antibodies seen in Graves’ are TPO (Thyroid peroxidase antibodies) and TG- Thyroglobulin antibodies.
Generally a healthy person should not have thyroid antibodies (or at least in very low levels). A person with thyroid autoimmune disorder produces a high level of antibodies.
Diagnostic test results for Graves’ disease are: low TSH, elevated thyroid hormone levels, presence of TSI and elevated RAI-U test (radioactive iodine uptake).