Thyroxine - Free (FT4)

Thyroxine or T4 is a thyroid hormone that regulates your body’s metabolism, temperature, blood pressure, heart rate, etc. It is produced along with the T3 hormone and plays an important role in the growth and development of the nervous system and the brain. T4 hormone exists in the blood in two forms: bound (attached to proteins) and free (not attached to proteins). Deranged levels of this hormone can result in either hyperthyroidism (the thyroid gland produces too much T4) or hypothyroidism (the thyroid gland produces less T4). 

The Thyroxine - Free (FT4) test measures the amount of free thyroxine hormone (T4), which is not attached to any protein. Your doctor may suggest this test if you show symptoms suggestive of hyperthyroidism, like increased appetite, weight loss, sweating, anxiety, tremors, etc., or hypothyroidism, like fatigue, weight gain, dry skin, constipation, etc.

No special preparations are needed for this test. Usually, you do not need to stop taking your thyroid medication before taking this test. However, do let your doctor know about all the medications you take as some of them can affect your thyroid test results. Biotin (Vitamin B7) is a commonly taken over-the-counter supplement that can lead to some aberrancy in your thyroid function tests even when the values are actually normal. Hence, avoid taking biotin 2 days before this test.

Test result ranges are approximate and may differ slightly between different labs depending on the methodology and laboratory guidelines. Talk to your doctor about your specific results. The test results will help them determine your medical condition, make recommendations for lifestyle modifications such as diet and exercise, evaluate whether or not medication will be required to manage your condition, and formulate an overall treatment plan.