Thyroid Hormone Tests

T3 (Triiodothyronine) Test, T4 (Thyroxine) Test, Thyroxine (T4) Test, Triiodothyronine (T3) Test

Results

Thyroid hormone tests are blood tests that check how well the thyroid gland is working.

Normal

Normal values may vary from lab to lab. Results are usually available within a few days.

Labs generally measure free T4 (FT4) levels, but also may measure total thyroxine (T4) and T3 uptake (T3U). Results of these thyroid hormone tests may be compared to your thyroid-stimulating hormone (TSH) results.

Thyroid hormone tests

Total thyroxine (T4):	9.8–22.6 micrograms per decilitre (mcg/dL) in newborns (1 to 14 days of age) 5.6–16.6 mcg/dL in babies and older children 5–14 mcg/dL in adults
Free thyroxine (FT4):	0.8–2.4 nanograms per decilitre (ng/dL)
Total triiodothyronine (T3):	32–250 ng/dL in newborns (1 to 14 days of age) 83–280 ng/dL in babies and older children 80–230 ng/dL in adults
Free triiodothyronine (FT3):	0.2–0.6 ng/dL
Free Thyroxine Index (FTI):	7.5–17.5 in newborns (1 to 14 days of age) 5.0–12.8 in babies and older children 4.2–13.0 in adults

Many conditions can change thyroid hormone levels. Your doctor will talk with you about any abnormal results that may be related to your symptoms and medical history.

High values

High thyroid hormone levels (hyperthyroidism) may be caused by:

• Diseases of the thyroid gland, such as Graves' disease, thyroiditis, or a goiter that contains one or more abnormal growths (nodules).
• Taking too much thyroid medicine.

Low values

Low thyroid hormone levels (hypothyroidism) may be caused by:

• Thyroid disease such as thyroiditis.
• Pituitary gland disease.
• Destruction of the thyroid gland by surgery or radiation.

Go to previous section	Go to top of page	Go to next section
Author:	Alison Allen Caroline Rea, RN, BS, MS	Last Updated: February 18, 2008
Medical Review:	Anne C. Poinier, MD - Internal Medicine Caroline S. Rhoads, MD - Internal Medicine David C.W. Lau, MD, PhD, FRCPC - Endocrinology & Metabolism
© 1995-2008 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.This information does not replace the advice of a doctor. Healthwise disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.