The range for normal values is 100 - 200 nanograms per deciliter (ng/dL).
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different specimens. Talk to your doctor about the meaning of your specific test results.
What Abnormal Results Mean
A higher-than-normal level of T3 may be a sign of:
A high level of T3 may occur in pregnancy or with the use of birth control pills or estrogen.
A lower-than-normal level may be due to:
Short- or long-term illness
Thyroiditis (swelling or inflammation of the thyroid gland -- Hashimoto disease is the most common type)
Underactive thyroid gland
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
Fainting or feeling light-headed
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)
Guber HA, Farag AF. Evaluation of endocrine function. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 24.
Salvatore D, Davies TF, Schlumberger MJ, et al. Thyroid physiology and diagnostic evaluation of patients with thyroid disorders. In: Melmed S, Polonsky KS, Larsen PR, et al., eds. Williams Textbook of Endocrinology. 12th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 11.
Brent Wisse, MD, Associate Professor of Medicine, Division of Metabolism, Endocrinology & Nutrition, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.