T4 Test

This test is used to measure the levels of total thyroxine (T4) in the blood. The thyroid gland produces hormones known as triiodothyronine (T3) and thyroxine (T4). These hormones help to control the rate at which energy is used in almost every tissue in the body.

Most of the thyroxine in the blood (>= 99.95%) is bound reversibly to various transport proteins; this is known as bound T4. The remaining thyroxine freely circulates in the blood (free T4) and is available to the body for use. During this test, the total thyroxine levels are measured (bound + free).

Importance of Thyroid Gland:

This test is usually done with other thyroid tests to determine if the thyroid gland is functioning normally. The thyroid gland is a part of the endocrine system. It produces and releases the thyroid hormones into the bloodstream. The hormones produced by the thyroid gland regulate various functions in the body including heart function, digestive function, bone maintenance, brain development, muscle control, metabolism (the rate at which the body uses energy), etc.

Why this test is performed?

This test is used to identify if the thyroid gland is hyperactive (hyperthyroidism) or underactive (hypothyroidism). Hyperthyroidism is a condition where the thyroid gland produces too many hormones. This condition may cause signs and symptoms such as a sudden weight loss, irritability, sweating, irregular heartbeats, etc. Hypothyroidism is a condition where the thyroid gland does not produce enough amount of hormones. This condition may cause signs and symptoms such as a sudden weight gain, dry skin, constipation, feeling cold, slow heart rate, etc. Your doctor may ask you to undergo this test if you are suffering from any such symptoms.

If you are suffering from a thyroid disorder and receiving treatment for the same, your doctor may advise you to undergo this test as part of routine monitoring as well as to determine the effectiveness of the treatment.

Frequency of Testing:

If you are a healthy individual above the age of 35, your doctor may advise you to undergo this test either on a yearly basis or every other year. If you have been diagnosed with a thyroid disorder, your doctor may advise you to undergo this test once every 3 months to once a year based on your clinical condition.

Precautions:

Drugs such as amiodarone, birth control pills, multivitamin pills, etc. may affect the results of this test. Hence, all medications should be reported to the doctor before undergoing this test.

If you are a healthy individual and the test results are in the normal range, then the thyroid gland is functioning normally and there is no need for medical intervention.

If you have been diagnosed with a thyroid disorder and the test results are in the normal range, then the treatment you are receiving is working effectively.

If the total thyroxine levels are above the normal range, it may be indicative of hyperthyroidism. Certain conditions such as Grave’s disease (an immune system disorder which results in the overproduction of thyroid hormones), thyroiditis (inflammation of the thyroid gland), toxic multinodular goiter, thyroid cancer, etc. may also be responsible for the increased levels of total thyroxine hormone in the blood.

If the level of total thyroxine is below the normal range, then it may be indicative of hypothyroidism, pituitary dysfunction, malnutrition, iodine deficiency, etc.

If the total thyroxine levels are above or below the normal range, consult your doctor immediately.