Thyroid Hormone Tests: Results
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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.
| Total thyroxine (T4): | 9.8–22.6 micrograms per deciliter (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 deciliter (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.
| Last updated: | December 03, 2007 |
|---|---|
| Author: | Caroline Rea, RN, BS, MS |
| Reviewed By: | Caroline S. Rhoads, MD - Internal Medicine, David C.W. Lau, MD, PhD, FRCPC - Endocrinology & Metabolism |
| Editors: | Maria G. Essig, MS, ELS, Pat Truman, MATC |
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