Triiodothyronine also is known as T3 is the active form of thyroid hormone. T4 also known as thyroxine is made in the thyroid gland. T4 is then sent peripherally through the system, and mainly the liver will convert T4 to T3. You can have all the T4 in your body, but if your T3 is low, then you will have symptoms of low thyroid.
If suspecting a case of low thyroid, thyroid disease, hypo or hyperthyroid your conventional doctor is going to run a TSH blood test. The TSH (Thyroid Stimulating Hormone) is a signal from the brain monitoring thyroid disease and the thyroid levels in the body.
To put it simple:
- If the thyroid levels are high, then the TSH is low.
- If your thyroid levels are low, then TSH is high.
As mentioned above the thyroid mainly makes T4, which is released into the blood and will travel in the body and be converted to the active form of thyroid, T3. Approximately 60% of this conversion occurs in the liver, about 20% is converted by gut flora and about 20% is converted by peripheral tissues, such as muscle.
As we have always talked about before, your primary care doctor is looking for a ‘disease.’ If you have a ‘disease,’ your GP, internist, or endocrinologist can save your life. In the case of thyroid, your conventional doctor is going to run a TSH and perhaps a T4. That is because they are looking for thyroid disease, not low levels of T3.
Many people with Low T3 get missed by their doctor because their TSH is in the normal range. They are told, “you are fine,” even though they do not feel fine.
How do you know if you have Low T3? You can do a blood test for Free T3. Free T3 is the bio-available thyroid hormone ready for use. In checking for Low T3, you want to check the free T3 levels, not the Total T3 levels. Total T3 levels in the blood represent all Free T3 and bound T3 levels. Testing for total T3 levels is not going to be accurate enough to find out if you have Low T3.
You may need to request blood testing for Low T3 from your doctor, or you may need to order it yourself if your doctor will not order it.
Blood tests checking for Low T3 Level:
- Free T4
- Free T3
This is where it gets a bit confusing. The reference range for Free T3 is broad.
Free T3 Reference Range:
- 2.3 to 4.4 (depending on the lab).
- If your Free T3 is under 3.0, we would consider this to be a Low T3 level.
Testing results we commonly see in patients with Low T3:
- TSH: normal range usually between 1.0-3.5 (reference range is .45-4.5)
- Free T4: 1.1-1.4 (reference range is .8-1.8)
- Free T3: 1.8-2.9 (reference range is 2.2-4.4)
Symptoms of Low T3:
- Weight gain or slow metabolism
- Dry skin
- Low mood
- Irregular periods
- Heavy periods
- Brain fog
- Hair loss
There are many treatments and ways to raise your Free T3 level. The goal is to get your T4 to better convert to T3. It is important to first make sure that it is Low T3 that is the culprit of your symptoms. The first step would be to visit your doctor to rule out other dysfunctions and disease states.
Running a full thyroid panel (including a Free T3) should be part of that evaluation. What happens if your doctor will not run a Free T3 blood test? Order it yourself. Sometimes insurance will not cover certain blood tests. Or your primary care providers are not validating your symptoms and will not run a Free T3 blood test. You can be your own healthcare advocate and order and pay for the test yourself.
If you would like to order your own thyroid panel, visit our online store and use the 25% off pricing code: THYROID
This has been extremely helpful to me! Thank you!
Dr. Maki says
I am glad you found this information helpful.
Lynne Jolly says
I believe I have a thyroid conversion problem now after 5 yrs on Levo. GP and endo doc haven’t tested my T3 . I will order my own tests. Thank you