The thyroid gland is located at the front of the neck and just below the Adam's apple. Although it is small, this organ plays a critical role in the body's endocrine system by releasing hormones that regulate metabolism. If the amount of hormones released by your thyroid is below the normal functioning level, you may experience symptoms of hypothyroidism. When thyroid hormone levels are too high, hyperthyroidism can result.
Tests
Doctors use blood tests to check thyroid hormone levels and to determine what, if any, medical treatment is required. Testing for thyroid-stimulating hormone, or TSH, indicates the level of a hormone produced by the pituitary gland that triggers thyroid activity. Tests for thyroxine, or T4, and triiodothyronine, or T3, directly measure the thyroid's hormone output. The ranges of what is considered normal thyroid function may vary slightly from laboratory to laboratory.
TSH Ranges
TSH test range results between 0.4 to 4.0 milli-international units per liter, or mIU/L, is considered normal for a person with no symptoms of thyroid disorder. The parameters are somewhat narrower for those who are prescribed medication for thyroid disease. A TSH level between 0.5 and 2.0 mIU/L indicates appropriate medical treatment of a patient with thyroid disorder, according to the UCLA Endocrine Surgery website. Those individuals with a TSH level over 2.0 mIU/L, even if asymptomatic, may be prone to developing hypothyroidism in the future, and should undergo periodic testing.
T4 Ranges
T4 blood test results between .5 to 11.2 micrograms per deciliter, or mcg/dL, indicate thyroid hormone levels within the normal range. High T4 levels, particularly in combination with low TSH levels, can be an indicator of hyperthyroidism caused by such conditions as thyroiditis or Grave's disease. Low T4 levels may be the result of hypothyroidism, as well as malnutrition or illness. T4 levels can be affected by certain drugs. Birth control pills, estrogen and methadone are among those drugs that can elevate T4 levels, while lithium, androgens and anabolic steroids may lower them.
T3 Ranges
A T3 test ranging between 100 to 200 nanograms per deciliter, or ng/dL, is considered normal. Low levels of T3 can indicate hypothyroidism, or may be the result of a long-term illness. High T3 levels may be caused by hyperthyroidism. Pregnancy can cause a temporary elevation of T3 levels due to the presence of higher-than-normal levels of a protein that carries T3 in the blood.
