A diagnosis of hyperthyroidism may be made when a doctor or nurse practitioner concludes that a patient's history, physical examination findings, blood test results, and radiographic study findings provide enough evidence to indicate that the tissue that makes up the patient's thyroid gland is producing and secreting excess amounts of thyroid hormone. In most situations, a diagnosis of hyperthyroidism is usually considered after an initial diagnosis of thyrotoxicosis has been confirmed through reliable blood tests that show that a patient's TSH level is suppressed below the lower limit of the reference range at the same time that thyroid hormone levels are increased above the upper limits of reference ranges.
There are different approaches that may be taken to determine whether the tissue that makes up a patient's thyroid gland is overactive. In some situations, a experienced doctor or nurse practitioner may rely on looking for specific clues while taking a patient's history and performing a physical examination. If there are specific symptoms or findings that point to a particular underlying disorder associated with the production and secretion of excess amounts of thyroid hormone, the doctor or nurse practitioner may be able to make a diagnosis of hyperthyroidism without any performing any further tests. This type of diagnosis, based on evidence derived from a history and physical examination, is called a clinical diagnosis.
In other situations it may be necessary to perform radiographic studies to determine whether the tissue that makes up a patient's thyroid gland is overactive. The study most commonly used to measure the activity of the thyroid gland is called a thyroid uptake study. This study provides a measurement of the thyroid gland's affinity for iodine. If used appropriately, a thyroid uptake study may help to distinguish true hyperthyroidism from other possible causes of thyrotoxicosis. A different radiographic study used to generate images of the thyroid gland is called a thyroid scan. The images generated during the acquisition of a thyroid scan reflect levels of activity in different parts of the thyroid gland. In the setting of a suspected diagnosis of hyperthyroidism, these images may provide clues that help to distinguish between different underlying disorders.