Hyperthyroidism is a common condition that affects the thyroid gland. It is diagnosed clinically based on signs and symptoms and findings of physical examination. The diagnosis is confirmed by blood tests for TSH and free T4 or free T4 index, radioactive iodine uptake test and thyroid scan.
Medical history and physical exam: A detailed history forms the first step in diagnosing hyperthyroidism. Your doctor will ask you questions regarding changes in your health and your symptoms. During the exam, your doctor will check for symptoms of hyperthyroidism such as a slight tremour in your fingers when they're extended, overactive reflexes, eye changes and warm, moist skin. The thyroid gland will be examined for changes and its movement as you swallow.
Blood tests: Diagnosis of hyperthyroidism can be confirmed with blood tests that assess the levels of thyroxine and TSH (thyroid stimulating hormone) in your blood. TSH is a hormone that controls synthesis of thyroid hormone (T4) in the body and the level of TSH is influenced by T4 level in the blood. When more T4 is made by the thyroid gland, less TSH is present in the blood. If the level of TSH is abnormally low, it means that you have hyperthyroidism i.e. your pituitary gland is being asked to make less TSH as the level of T4 is high in the blood. High levels of thyroid hormones and low or non-existent amounts of TSH indicate an overactive thyroid. It is important to measure the levels of thyroid hormone and TSH particularly in older adults as they may not have classic symptoms of hyperthyroidism.
If blood tests are suggestive of hyperthyroidism, one of the following tests may be done to find the reason for overactive thyroid:
Radioactive iodine uptake test: To do this test, you will be given a small oral dose of radioactive iodine (radioiodine). Iodine is an essential component needed to make the thyroid hormone. It is actively absorbed by the thyroid gland. A few hours (two, six or 24 hours) after ingestion of radioactive iodine (radioiodine), the uptake of iodine by the thyroid gland can be determined. If the uptake of radioiodine is high, it indicates that your thyroid gland is producing an excess of thyroxine. In most cases, it is caused by either Graves' disease or hyper functioning nodules. A person with hyperthyroidism and low radioiodine uptake is more likely to have thyroiditis. Diagnosing the cause of hyperthyroidism helps the doctor to plan the appropriate treatment.
Thyroid scan: In this test, a radioactive isotope is injected into the vein (most commonly on the inside of your elbow or sometimes, into a vein in hand). A special camera is used to produce an image of your thyroid on a computer screen. In some cases, it may be done as a part of a radioactive iodine uptake test. The test can determine the uptake of radioactive isotope by the thyroid gland.