Why Test T3? And What’s An IDEAL Lab Result?

If you continue to struggle with hypothyroidism it’s vital to test T3 as it is one of the best indicators of thyroid function. Let me explain more.

T3 is the body’s most biologically active thyroid hormone. For this reason, a low FT3 result is useful to diagnose hypothyroidism.

As you can imagine it’s important to address a low T3 problem. You will feel so much better when you have an optimal amount of FT3. This is the key thyroid hormone that boosts metabolism to fight fatigue and other annoying hypothyroid symptoms.

According to the Society of Endocrinology, “T3 is a thyroid hormone that plays vital roles in the body’s metabolic rate, heart and digestive functions, muscle control, brain development and function, and the maintenance of bones.”

So it’s definitely something you want to check if you continue to struggle with thyroid dysfunction.

WHY Testing ‘Free’ T3 Is So Important

The thyroid constantly releases hormones into the blood so a blood test is a simple way to check how much the thyroid is producing.

Free triiodothyronine (FT3) test: Low levels are a sign of an underactive thyroid. When you test ‘free’ T3 you are measuring the amount of T3 that is unbound and therefore free to do its job. In other words, by testing free T3 (FT3) you are specifically measuring the active amount of T3 that is working in the body.

In Australia the standard reference range is: 4.0-8.0 pmol/L. An ideal result shows FT3 is above 4.0 – 4.5 pmol/L.

Are you finding it hard to find a doctor who will run the lab tests you want? I recommend you get proactive and order the lab tests you want online. It’s now so much easier with companies such as iscreen, Australia or True Health Labs, USA. These pathology companies offer a range of thyroid tests.

The Free T3 Test Should Be Done As Part of a Complete Thyroid Panel

Comprehensive testing is essential to properly assess overall thyroid function. There are 5 basic thyroid lab tests you need to know about;

  • Thyroid stimulating hormone (TSH)
  • Free T4 (FT4)
  • Free T3 (FT3)
  • Reverse T3 (RT3)
  • Thyroid antibodies: thyroid peroxidase Abs (TPO Ab) + antithyroglobulin Abs (ATG Ab)

You can learn more about comprehensive testing here: The Top 5 Thyroid Tests? Discover The Best Tests To Discuss With Your Doctor

Lab Results Should Be Considered Along With How You Feel

When discussing your lab report with your healthcare practitioner your results should be carefully considered with how you feel.

Low thyroid symptoms are significant indicators that your thyroid is not working well. The most common symptoms include fatigue, feeling the cold, dry skin and hair, low libido, menstrual irregularities, mood changes, low blood pressure, heart palpitations, hair loss, muscle weakness, and stubborn weight gain.

If you have a history of thyroid problems in your family you should definitely mention this to your healthcare practitioner.

Before You Test T3

Medications containing T4, T4/T3 combination, or single T3 are usually prescribed to restore the sub-optimal level of thyroid hormones.

Although T3 activity is often discussed in relation to weight management, you should not take a single T3 medication for the sole purpose of assisting weight loss. Taking single T3 medication does carry some risks. Too much T3 can cause serious side effects such as a rapid heart rate and agitation.


You and your hormones. Thyroid gland. Society for Endocrinology. Last reviewed: Mar 2018. Link

Mullur R, Liu YY, Brent GA. Thyroid hormone regulation of metabolism. Physiol Rev. 2014;94(2):355–382.

Please note this post contains affiliate links. This means that a special tracking code is used and I may make a small commission if you go ahead and order the thyroid tests you need. The price of the tests is the same for you whether it’s an affiliate link or not, and using affiliate links helps me to maintain this website. To find out more about my affiliate policy please refer to my Terms of Service.


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