T4 test

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Blood test

Thyroxine test

Normal values vary among different laboratories. A typical normal range is: 4.5 to 11.2 mcg/dL (micrograms per deciliter).

Greater-than-normal levels of T4 along with low levels of TSH may indicate hyperthyroid conditions, such as:

• Graves' disease
• toxic multinodular goiter
• subacute or chronic thyroiditis
• early Hashimoto's disease
• iodine-induced hyperthyroidism
• germ cell tumors
• trophoblastic disease

Lower-than-normal levels of T4 may indicate:

• hypothyroidism (including Hashimoto's disease , cretinism, myxedema, goitrous diseases, scleroderma, amyloid goiter, or hemochromatosis following neck irradiation for head and neck cancer)
• malnutrition or fasting
• illness throughout the body
• use of certain prescribed medication, including dexamethasone, propranolol, lithium, iodine, methimazole, propylthiouracil, interferon alfa, interleukin-2, and amiodarone

Additional conditions under which the test may be performed:

• hypopituitarism
• hypothyroidism - primary
• hypothyroidism - secondary
• thyrotoxic periodic paralysis

Review Date: 01/18/2006
Reviewed By: Nikheel S. Kolatkar, MD, Clinical and Research Fellow, Division of Endocrinology, Diabetes, and Hypertension, Brigham and Women's Hospital, Harvard Medical School, Boston, MA. Review provided by VeriMed Healthcare Network.