Graves' Disease

Tests
In addition to thyroid function tests (TSH, T4, T3), additional tests that can help in the diagnosis include:

Radioactive iodine uptake: A capsule or “cocktail” containing a measured amount of radioactive iodine is swallowed; iodine is a critical component of thyroid hormones. The iodine accumulates in the thyroid; more accumulates when the gland is overactive, as occurs in Graves’ disease. After a specified amount of time, a probe similar to a Geiger counter is placed over the thyroid and the amount of radioactivity is compared to the amount that was given.
Thyroid stimulating immunoglobulin (TSI): This immunoglobulin is an autoantibody in the blood that acts like TSH at its receptor on the thyroid gland, stimulating the thyroid to produce increased amounts of hormone. Another test to detect thyroid stimulating antibodies, though not as specific as TSI, is a test for Thyroid stimulating hormone receptor antibody (TRAb).
Anti-thyroid peroxidase antibody (anti-TPO): This autoantibody is found in most people with Graves’ disease, as well as in Hashimoto’s thyroiditis.