The three types of thyroid blood tests are the total thyroxine test, the free thyroxine test and the triiodothyronine test. Each of these tests can determine whether the thyroid is releasing the appropriate number of hormones in the body. The blood tests also can be used to monitor whether a thyroid treatment plan is working and can be a first step in determining whether thyroid diseases or disorders are present.
The thyroid gland is located in front of the trachea, or windpipe, and below the voice box. Iodine from food is used to make hormones called thyroxine and triiodothyronine, also known as T4 and T3, respectively. The thyroid stores and releases these hormones as the body needs them.
Thyroid blood tests in adults are important because the thyroid gland produces the hormones that regulate the body’s metabolism. In babies, the thyroid helps in brain development. It often is recommended that thyroid functioning is tested in babies, because deficiencies can lead to mental retardation. In older children, the thyroid helps regulate normal growth.
If the blood tests determine high hormone levels in the thyroid, it can be an indication of a goiter, abnormal growths or nodules on the thyroid, Graves’ disease or thyroiditis. Low levels of thyroid hormones can indicate pituitary disease, thyroiditis or damage to the thyroid from surgery. If any of these indicators are present, a doctor might recommend further tests or prescribe thyroid medications.
There is little to no risk associated with thyroid blood tests. The greatest discomfort usually is a small bruise or tenderness at the site where the needle entered the skin. If the area becomes swollen, a warm compress usually will alleviate any swelling. Bleeding disorders sometimes can present a problem with clotting after the blood test.
Thyroid blood tests will show elevated thyroid hormones in hyperthyroidism. Other symptoms can include thinning hair, a rapid heart rate, an enlarged thyroid and eye puffiness. Blood tests usually show decreased thyroid hormone levels in hypothyroidism. Other possible symptoms include fatigue, dry skin and intolerance to cold.
Although thyroid blood tests can indicate hormone levels, they cannot determine the cause of abnormal hormone levels. Additional tests might be required to determine the cause. This can include additional ultrasound examinations. In some cases, additional blood tests are ordered to detect the presence of thyroid antibodies.