Your Thyroid: Why Test T3?

Issue # 116 July 11, 2013


Welcome to KnowYourThyroid.

Today Louise O’Connor will explain why it is important to have your T3 levels tested, plus she will explain the ongoing debate on which hormones should be tested and what range is considered normal.

Then, in today’s Check It Out! take a few minutes to look at Louise’s Natural Thyroid Diet. It is an all natural diet to nourish your thyroid.



Why test T3?

By Louise O’Connor


Triiodothyronine (T3) is the thyroid hormone that is central to controlling the body’s metabolic rate. Even though T3 is normally present in smaller amounts compared to thyroxine (T4) it’s the more active thyroid hormone that helps ‘rev’ up your body. Low T3 is associated with sluggish metabolism and many of the indicators of a low thyroid.

Adequate T3 assists fat burning which aids weight loss. This thyroid hormone is also involved in stimulating energy production and protects against heart palpitations. A single test of available T3 therefore provides the best clue as to how your thyroid is working.


When discussing a T3 test with your healthcare practitioner it’s best to specify testing free T3. The majority of T3 in the blood is carried by a protein compound called thyroxine binding globulin. A small amount of T3 is unattached and ‘free’ to do its job. A T3 blood test usually measures both bound and free T3. When you test free T3 you are measuring the active component.

The Testing Controversy

Getting a diagnosis of hypothyroidism has sparked an ongoing debate on what thyroid hormones should be tested and the levels that will reveal a thyroid hormone deficiency. Generally,  thyroid stimulating hormone (TSH) is the preferred initial test performed by medical practitioners to diagnose a thyroid disorder. TSH is produced in the brain’s pituitary gland. A pituitary that produces excess TSH indicates that the thyroid is functioning below par and therefore requires more stimulation than usual. The problem lies in defining a ‘normal’ range for TSH. I have found that even when TSH is considered ‘normal’ many individuals experience symptoms of hypothyroidism. On testing TSH should ideally be less than 2.0 mIU/L.

An accurate assessment of thyroid health can only be achieved with comprehensive testing. A measure of free T4 and free T3 alongside TSH is essential. In addition, a measure of thyroid antibody levels will rule out Hashimoto’s thyroiditis. This is a common thyroid disorder that tends to run in families and affects women more than men.

If you have swelling or discomfort around your throat your healthcare practitioner should also perform a physical examination. If required a thyroid ultrasound will provide a more in depth investigation of your thyroid.


Khandelwal D, Tandon N. Overt and subclinical hypothyroidism: who to treat and how. Drugs. 2012 Jan 1;72(1):17-33.

MedlinePlus. TSH test.

myDr. Thyroid Gland Disorders.


Louise O’Connor is a leading Australian Naturopath & Wellness Coach who specialised in thyroid health. The Natural Thyroid Diet is her top-selling e-book that contains a wealth of information on recovering your thyroid health from a holistic, Naturopathic viewpoint. Louise believes that when you are empowered with credible information and an awareness of new opportunities it really is possible for you to finally take control of your thyroid health… to reclaim the vibrant health YOU deserve!


Check It Out!


To help you on your way to improving your thyroid health, be sure to check out Louise’s ebook:

The Natural Thyroid Diet