T4 test

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Thyroxine test

A typical normal range is 4.5 to 11.2 micrograms per deciliter (mcg/dL).

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

Greater than normal levels of T4 along with low levels of TSH may be due to conditions that involve an overactive thyroid, including:

• Early Hashimoto's disease
• Graves disease
• Germ cell tumors
• High levels of the protein that carries T4 in the blood (can occur with pregnancy, use of birth control pills or estrogen, liver disease, and as part of an inherited condition)
• Iodine-induced hyperthyroidism
• Subacute or chronic thyroiditis
• Toxic multinodular goiter
• Trophoblastic disease

Lower than normal levels of T4 may indicate:

• Hypothyroidism (including Hashimoto's disease and several other disorders involving an underactive thyroid)
• Illness
• Malnutrition or fasting
• Use of certain medications

Review Date: 04/20/2010
Reviewed By: Ari S. Eckman, MD, Division of Endocrinology and Metabolism, Johns Hopkins School of Medicine, Baltimore, MD. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org).

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