Normal ranges for thyroid tests vary between laboratories, according to WebMD. There are also multiple kinds of thyroid tests, which measure thyroid function or thyroid hormone levels in different ways. Normal values for these tests also vary.
Blood tests for thyroid function measure thyroid stimulating hormone, or TSH; thyroxine, or T4; and triiodothyronine, or T3, according to the American Thyroid Association. TSH is typically too high in people with hypothyroidism and too low in people with hyperthyroidism. Testing T3 or T4 levels in addition to testing TSH levels can help to evaluate the severity of thyroid dysfunction and identify the cause of a thyroid problem.
Normal levels for tests of TSH, T3, and T4 vary depending on the laboratory doing the testing, according to WebMD. For most laboratories, the normal range of TSH in adults is between 0.4 and 4.2 milliunits per liter of blood. There are multiple ways to measure T3 and T4. For adults, total T4 normally ranges between 5.4 and 11.5 micrograms per deciliter of blood, and free T4 ranges between 0.7 and 2.0 nanograms per deciliter of blood. A normal range for total T3 in adults is usually 80 to 200 nanograms per deciliter of blood, and a normal range for free T3 is about 260 to 480 picograms per deciliter of blood. Normal ranges are different for infants, children and teenagers.
As of 2013, some doctors and researchers think that the these ranges require adjustments, reports the American Association for Clinical Chemistry, making the upper normal limit as low as 3.0 milliunits per liter. Other experts argue that there is no evidence that treating people whose TSH levels are in this range is beneficial; they think that labelling these people as having a thyroid dysfunction is inaccurate.