Thyroxine, Total

What is T4 Total?

Our thyroid gland is responsible for making two major hormones that are T4 and T3. Most T4 hormones are found in the blood and bound to proteins, the rest roam freely in our system. They stimulate the entire body’s cellular system and boost oxygen consumption, this will boost the metabolism, growth and development. What makes the T4 hormones different from the T3 hormones is that the latter is five times more effective; however, 90% of T3 are converted from T4 hormones.

The American Thyroid Association explains that T4, T4 Total, is found in two forms in our body. The first form is when T4 are attached to proteins and cannot access the various tissues that are in need of thyroid hormones. The second form is free T4 hormones that are capable of entering the many target organs and providing them with the needed thyroid hormone. This free T4 is the most important form since it can help explain how the thyroid gland is functioning.

T4 levels, explain how much is being converted to T3, which gives an idea about how the body is processing both hormones (T4 and T3). When the hypothalamus, pituitary and thyroid organs are functioning well, the T4 production is regulated to keep the levels stable.

Why take the T4 Total test?

The T4 Total test is also referred to as T4 Blood Test, Total Tetraiodothyronine Blood Test, or Total Thyroxine Blood Test. This test is recommended as a follow-up to the TSH and free T3 test to assess the thyroid functions. It is also a good indicator of a healthy thyroid early in puberty. It helps differentiate between primary and secondary hypogonadism as well as explaining why women are growing excessive hair in unwanted areas (masculinization of women). The T4 test is an important indicator for infertility, low sex drive and less common menstrual cycles. It may also explain the reason behind abnormal uterine bleeding.

What can cause the levels of T4 Total to rise?

The Free T4 test results can be affected by factors other than the malfunctioning of the thyroid, pituitary or hypothalamus. Being pregnant or following a rigid work-out can interfere with the results. Also, age and a person’s dietary habits can have an impact on the results of the Free T4 test.

Some medications can influence results, such as herbal supplements, vitamins, over-the-counter medicines and others. Make sure you provide your doctor with the full list to ensure you are not misdiagnosed.

What your T4 Total test results mean?

Adults thyroxine (both free and bound) levels need to be between 5.4 and 11.5 mg per deciliters. The University of Michigan Health System has it set to be between 5 and 13.5 microgram/dL. Values can change from one laboratory to another.

Results that are higher than the upper limit, can indicate hyperthyroidism, acute psychiatric illness, high intake of iodine, Hyperemesis gravidarum, hepatitis, Grave’s disease or Thyrotoxicosis. Results that are lower than 5 micrograms/dL could be caused by hypothyroidism or other conditions that cause a decrease in TBG.

Total T4 test results should not be analyzed on their own, other thyroid tests are needed to help a physician make a proper diagnosis.

Where can I get a T4 Total 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