Figuring out that you have hyperthyroidism isn't always easy. Pinpointing the cause is even tougher. Lower than normal levels of TSH generally suggest an overactive thyroid, but your doctor may need other tests as well as your self-reported symptoms before reaching a conclusive diagnosis.

In some people, the tests may all come back normal, despite the presence of bothersome symptoms. If that happens to you, make sure to request follow-up testing in six months. But if the tests are not normal, you will probably be given a diagnosis of some form of hyperthyroidism.

Mild (Subclinical) Hyperthyroidism

If your TSH levels are lower than normal but your free T4 and free T3 tests are normal or slightly high, you are said to have mild or sub-clinical hyperthyroidism. Experts don't always agree on whether you need treatment at this point, but routine monitoring and evaluations are important regardless.

Detecting subclinical hyperthyroidism is especially difficult. The only clue might be a slightly lower than normal TSH level. Nonetheless, treatment can be important, especially in older patients, who are at greater risk for heart problems and osteoporosis.

Hyperthyroidism

If your TSH level is low or nonexistent and your free T4 and T3 levels are normal to high, you will probably be diagnosed with basic hyperthyroidism.

Graves' Disease

If you test positive for TSI antibodies and have a low or nonexistent TSH level and normal to high free T4 and T3 levels, you may be diagnosed with Graves' disease. Your scan will show increased radioactivity throughout the gland. You may also have TPO antibodies, but because TPO also occurs in Hashimoto's disease, your doctor will need to make sure to perform the TSI antibodies test to ensure an accurate diagnosis.

Pituitary Hyperthyroidism

Rarely, tumors on the pituitary gland called adenomas may secrete TSH, causing the thyroid to produce too much thyroid hormone. In this case, your TSH is high, and your free T4 and free T3 tend to be elevated.