T4 (Thyroxine), Free

What is T4 Free?

Our thyroid gland is a small butterfly shaped organ that is located at the base of our throat. It produces two major hormones that are the thyroxine (T4) and the triiodothyronine (T3). Most of these two hormones are bound to proteins in our blood. Whatever it is not attached to proteins, is free.

Why take the T4 Free test?

A free T4 test is advised when individuals have some symptoms of hyperthyroidism or hypothyroidism. The signs and symptoms of hyperthyroidism include fast heart rate, anxiety, weight loss, not being able to sleep, tremors in hands, weakness, diarrhea, light sensitivities and puffiness. Signs of hypothyroidism include weight gain, dry skin, constipation, cold intolerance, puffy skin, hair loss and fatigue.

Those who have goiter (enlarged thyroid gland) or a nodule on his/her gland need to check their free T4 levels that can also help evaluate your thyroid function, as well as diagnose the previously mentioned conditions. It is also a great way to monitor how effective a thyroid treatment is progressing. In newborns, it is used to detect congenital hypothyroidism. Also, the free T4 test is recommended for those who might have an autoimmune thyroid disease. Finally, this test can help distinguish between thyroid disorders, monitor individuals with thyroid cancer and the effectiveness of the administered therapy, and evaluate the function of the pituitary gland.

What can cause the levels of T4 Free to rise?

Being pregnant, having high estrogen levels and liver problems can sabotage your free T4 levels. Supplements that are used for hair and nails, as well as over the counter pills can affect your thyroid testing. Multivitamins can have the same effect.

What your T4 Free test results mean?

The normal values of free T4 range from 0.9 to 2.3 ng/dL. If your values are lower than 0.9; then, it may be caused by hypothyroidism, severe acute illnesses, malnutrition, fasting, or using some medications.

If your results are above 2.3; then, it may be due to hyperthyroidism. The best thyroid function analysis is when you combine results of TSH, free T4 and Free T3 or Total T3. Here are the example findings for illustrative purposes:

1. If TSH, Free T4 and Free T3 are within the normal range; then, you most likely have a good functioning thyroid gland.
2. If TSH and Free T4 are normal or lower than the normal range, and the Free T3 levels are lower than average; then, you most likely have a normal adjustment in your thyroid function due to an illness.
3. If TSH is increased and both Free T4 and Free T3/Total T3 are within normal ranges; then, you might have subclinical hypothyroidism. This means that the person who has hypothyroidism is not given the right dose of treatment.
4. When TSH is increased and both Free T4 and Free T3 are decreased; then, hypothyroidism is a possibility potentially caused by a problem in the thyroid itself.
5. When TSH is normal or increased and both Free T4 and Free/Total T3 are increased; then, you may have hyperthyroidism.
6. If TSH is decreased and both Free T4 and Free/Total T3 are within normal range; then, you may have subclinical hyperthyroidism. This means that too much thyroid hormone is being given to a person who has hypothyroidism.
7. If TSH is decreased, Free T4 is within normal ranges and Free T3/Total T3 are increased; then, you may have hyperthyroidism.
8. If TSH is above normal values, and both Free T4 and Free/Total T3 are higher than average; then, you may have hyperthyroidism caused by the thyroid gland making high levels of thyroid hormones. This is referred to as primary hyperthyroidism.
9. If TSH, Free T4 and Free/Total T3 are below normal ranges; then, you may have hypothyroidism caused by a hypothalamus or pituitary gland malfunction.

Where can I get a T4 Free test near me?

Please use our Lab Locator to find find a convenient testing location.

Reviewed By: Dr. Kurt Kloss, MD
Last Reviewed Date: May 24, 2019