Diagnosing Hyperthyroidism: Overactivity of the Thyroid Gland

Part 3: Making the diagnosis of hyperthyroidism

Written by James Norman MD, FACS, FACE

The actual diagnosis of hyperthyroidism is easy to make once its possibility is entertained. Accurate and widely available blood tests can confirm or rule out the diagnosis quite easily within a day or two. Levels of the thyroid hormones themselves, T4 and T3, are measured in blood, and one or both must be high for this diagnosis to be made.

It is also useful to measure the level of thyroid-stimulating hormone (TSH). This hormone is secreted from the pituitary gland (shown in orange) with the purpose of stimulating the thyroid to produce thyroid hormone. The pituitary constantly monitors our thyroid hormone levels, and if it senses the slightest excess of thyroid hormone in blood, it stops producing TSH. Consequently, a low blood TSH strongly suggests that the thyroid is overproducing hormone on its own.

Other special tests are occasionally use to distinguish among the various causes of hyperthyroidism. Because the thyroid gland normally takes up iodine in order to make thyroid hormones, measuring how much radioactive iodine or technetium is captured by the gland can be a very useful way to measure its function. The dose of radiation with these tests is very small and has no side effects. Such radioactive thyroid scan and uptake tests are often essential to know what treatment should be used in a patient with hyperthyroidism, and it's especially important if your doctor thinks your hyperthyroidism is caused by Graves' disease.

Common tests used to diagnose hyperthyroidism


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Hyperthyroidism: Overactivity of the Thyroid Gland