How is hyperthyroidism diagnosed?

If your physician suspects that you have hyperthyroidism, diagnosis is
usually a simple matter. A physical examination usually detects an
enlarged thyroid gland and a rapid pulse. The physician will also look
for moist, smooth skin and a tremor of your fingertips. Your reflexes are
likely to be fast, and your eyes may have some abnormalities if you have
Graves’ disease.
The diagnosis of hyperthyroidism will be confirmed by laboratory tests
that measure the amount of thyroid hormones— thyroxine (T4) and
triiodothyronine (T3)—and thyroid-stimulating hormone (TSH) in your
blood. A high level of thyroid hormone in the blood plus a low level of
TSH is common with an overactive thyroid gland. If blood tests show
that your thyroid is overactive, your doctor may want to obtain a picture
of your thyroid (a thyroid scan). The scan will find out if your entire
thyroid gland is overactive or whether you have a toxic nodular goiter
or thyroiditis (thyroid inflammation). A test that measures the ability of
the gland to collect iodine may be done at the same time.