How to use The Total T3 Lab Test to Help Evaluate your Thyroid

How to use The Total T3 Lab Test to Help Evaluate your Thyroid

Total T3 is one of many thyroid lab tests but it's one that not many patients are aware of. 

I've been successfully using total T3 in many patients and I feel that it is an invaluable tool to help you completely understand how your body is utilizing thyroid hormone. 

Article highlights:

  • Total T3 is a measurement of both free and bound T3 in your body. 
  • T3 is the single most important thyroid lab test you can order because T3 is the most important thyroid hormone. 
  • Optimizing your T3 may help you feel better, lose weight, and reduce your symptoms of hypothyroidism.
  • You should optimize your total T3 to the top 30% of the reference range but be cautious of making it go higher.


What Exactly is Total T3?

Before we jump in let me provide some quick information. 

All of my articles contain links to clinical studies which help provide further information on the claims that I make in my articles. 

Unfortunately, there just isn't a lot of research when it comes to total T3. 

Much of this has to do with the current thyroid treatment paradigm which focuses on other lab tests such as the TSH and the free T4. 

There are more studies on those topics than on T3, especially total T3. 

With that in mind, I'm going to focus on how I look at this particular test and how why I believe that it has value to you as an individual.

Most of the information I will be presenting here is based on my own personal experience in using this lab test and in helping treat many patients. 

So, back to our regular discussion. 

What exactly is total T3?

Total T3 is a simple thyroid lab test (one of many, by the way), which is used to give you information on how much T3 thyroid hormone is in your bloodstream. 

The idea is that the more T3 available, the more likely your thyroid is to work. 

This simple logic is why every single thyroid patient should have their thyroid hormone levels tested in addition to testing the TSH!

Do not neglect these tests. 

Total T3, along with free T3, is perhaps the single most important thyroid tests that you can order because they give you the most information about your thyroid. 

Even if you don't know much about your thyroid you should remember this:

T3 is the most biologically active thyroid hormone in your body. 


Because T3 is the main way that thyroid hormone influences your cells and turns on the right genes. 

If you don't have sufficient T3 in your body (total or free) you will simply not feel well. 

There's much more to this concept, but I want to keep it brief for purposes of this discussion. 

If you want to dive into more detail you can find more information on free T4 here and TSH here which will help you understand how these lab tests fit into the greater picture. 

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I've found that these 10 foods cause the most problems for thyroid patients. Learn which foods you should absolutely be avoiding if you have thyroid disease of any type. 

How to Calculate "Optimal" Free T4, Free T3, & Reverse T3 Ratio: 

Calculating these ratios is important because it can help you determine if your efforts are on the right track and whether or not your medications are working. 

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Free T3 vs Total T3

Total T3 is a completely different test and should be differentiated from free T3. 

Both tests are important, but each test gives you different (but useful) information. 

Often times, doctors put more emphasis on the concentration of free hormones when compared to the total concentration of hormones. 

Why is this?

Because we know, and this is true for total T3, that the free component of any hormone is much more active (1) compared to the bound or "total" concentration of protein in the body. 

Thyroid hormone circulates through your body in one of two ways:

#1. Bound to proteins which act to stabilize and prevent the decay of thyroid hormone.

And #2. Free and unbound are available to be used by the body at a moments notice. 

Your body uses this system to help prevent the unnecessary use of thyroid hormone and to save it for the tissues that really need it. 

If all of your hormone was free and active then your body would have a hard time saving it for certain tissues. 

So, instead, your body binds up 99% of the thyroid hormone (2) in your blood and only leaves a small fraction, less than 1% (0.04% to be exact (3)), free and active. 

In this way, your body creates a system which is in equilibrium. 

When you test your free T3 you are testing for the incredibly small, but incredibly active, amount of thyroid hormone in your body. 

Your total T3, on the other hand, represents both the free and total amount and gives you a bigger picture as to what is happening with T3 in your body. 

This is very important because it's possible for your body to have a sufficient amount of total T3 but an insufficient amount of free T3 or vice versa. 

But you'd never know the difference if you only look at one marker. 

I consider free T3 to be a valuable tool in assessing the short term availability of T3 in your system. 

Total T3 represents a more stable and long-term picture of T3 in the body. 

Free T4 vs Total T3

If total T3 is so important then why do doctors order free T4 instead?

Great question.

Let's break it down so you understand what your doctor is thinking. 

Doctors know, or at least they should, that T4 is considered a pro-hormone and it's primary value comes from being a precursor hormone to T3. 

Your body makes most of the T3 by converting it directly from the stores of T4 in your body (4). 

Put another way:

T4 is only important because it helps your body produce T3. 

Doctors know this and they make the assumption that if your body has enough T4 that your body will automatically produce enough T3. 

t4 to t3 conversion in the body

This logically makes sense, but it's not what we see in the real world due to the fact that so many variables influence this conversion process (5). 

I won't get into that topic here, but you can read more about the various conditions which blunt this conversion process

Free T4 is a measurement of the amount of T4 which is free and active in your body and which can be used by your cells to be turned into T3. 

This number is important because it has potential, but not because it has activity by itself (6). 

This doesn't mean that your free T4 is unimportant, on the contrary. 

It's very important, but it's not AS important as your total T3. 

But testing your free T4, if used along with the Total T3 and reverse T3, can help you understand if your body is taking that T4 and converting it into T3 at an appropriate rate. 

Reference Ranges for Total T3 & What They Mean

Let's take a minute to talk about references ranges and where you want your numbers to be. 

First off:

The reference range you see on your own labs may be slightly different compared to the values I'm showing here and that's okay. 

Each lab creates their reference ranges based on the local population, so they may be slightly different. 

Just do your best to compare your values to those I have listed here with a focus on the "percentage" range that I recommend. 


These values really only apply to those people who are actively taking thyroid medication

The range of "normal" is much broader for those people who aren't on thyroid medication. 

The standard reference range for T3 ranges from 76 to 181 ng/dL. 

If you are taking thyroid medication you want your result to be in the top 30% of the reference range

By being in this area you will ensure that your body has sufficient T3 (both total and free T3) to do the work that it needs to. 

To further clarify this range, let's look at a number of examples. 

Example of a low Total T3:

total T3 reference range

The first example is one of obviously low total T3. 

This patient has a Total T3 of 75 which is flagged as low. 

In cases such as these, priority should be placed on the total T3 to try and increase it dramatically because most people with a level this low will be symptomatic (fatigue, weight gain, etc.). 

Example of a low-normal Total T3:

low normal total T3

Perhaps a more common problem that many patients will face is the idea of a low but normal total T3. 

The example I've listed above illustrates this perfectly. 

Even though the total T3 is 91 (and still within the total reference range), it's on the low side of that range. 

People who find that they have a "low but normal" total T3 will often be symptomatic much like those people with a grossly low T3 level. 

The idea here is to bring that level up with the use of thyroid medications. 

Example of an "optimal" Total T3:

optimal total t3 for weight loss

My experience has shown me that most people do well when their total T3 is right around the tippy top of the total reference range. 

You can see this result, at 171 ng/dL, is very close to that high end of the range which is 181 ng/dL. 

I find that most people feel great and optimal at levels such as this (7). 

Ideally, you'll want to adjust your medication to get you there which may take some trial and error. 

You'll also want to try and get here without suppressing your TSH to a very low level

Example of a high Total T3:

elevated Total T3 example

Lastly, we also need to talk about what constitutes a high total T3. 

The good news is, much like a low total T3, a high total T3 is easy to spot. 

When high, your total T3 is will be flagged as much and you will often experience some set of symptoms consistent with hyperthyroidism (anxiety, heart palpitations, etc.). 

You can sometimes get away with having a high free T3 due to reasons such as when your medication was taken in relation to your lab tests, but you should never have a sustained high total T3. 

*Note: all of these lab results are from patients that I have personally treated.

Putting the Picture Together

Now that you understand the importance of total T3, how are you supposed to use it to help guide your treatment?

The answer is relatively simple. 

You should focus on therapies which help preserve your total T3 and maintain a high (but not overly high) total T3 in your body. 

Because T3 is one of the best measurements of thyroid status in the body, you can use this test to help you understand how well (or not) your body is utilizing thyroid hormone. 

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For instance:

Let's imagine a scenario in which you are someone who is suffering from hypothyroidism but who has a normal TSH and a normal free T4. 

From the perspective of your doctor, you are "treated" and any symptoms that you are experiencing can and should be chalked up to some other cause (this is around the time that patients get diagnosed with things like depression, or "aging").

The only problem is that unless you order the total T3 (and free T3) you can't accurately make that assumption. 

In this hypothetical instance, most of you will find that as you order your total T3 you will find that it is either grossly low or on the very low-end of the reference range. 

And, when you put this into context with other your other lab tests and your symptoms you will often find that it helps explain the full picture. 

If your TSH is normal and your free T4 is normal but your total T3 is low, then that is a problem that must be addressed. 

Your total T3 should take precedence over other "normal" thyroid tests because it carries more weight than they do. 

My personal recommendation is that each and every person who suspects they have thyroid problems and those who know they do have thyroid problems should get a complete thyroid lab test which includes the total T3. 

These tests may not be necessary each and every time that you check the status of your thyroid via lab tests, but they should be required for your initial evaluation. 


If you are someone with thyroid disease then you should have your total T3 evaluated. 

This is especially true if you are taking any type of thyroid medication including T4 only thyroid medications. 

By checking your total T3 you will have more information about how your body is processing and utilizing thyroid hormone. 

Total T3 gives you an idea as to how much free and active T3 is in your body as well as bound and inactive T3. 

My recommendation is to try and optimize your total T3 to the top 30% of the reference range while maintaining a non suppressed TSH. 

Now I want to hear from you:

Have you had your total T3 tested?

What values did you get?

How are you feeling?

Are you having trouble getting a doctor to order this test?

Leave your questions, comments or experiences below! 

References (Click to Expand)

why the total t3 thyroid lab test is so important

Dr. Westin Childs

About Dr. Westin Childs

Hey! I'm Westin Childs D.O. (former Osteopathic Physician). I don't practice medicine anymore and instead specialize in helping people like YOU who have thyroid problems, hormone imbalances, and weight loss resistance. I love to write and share what I've learned over the years. I also happen to formulate the best supplements on the market (well, at least in my opinion!) and I'm proud to say that over 45,000+ people have used them over the last 4.5 years. You can read more about my own personal health journey and why I am so passionate about what I do here.

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