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 few are more important. 

Unfortunately, most thyroid patients aren’t even aware that it exists and even fewer have had it tested! 

This creates a big problem when trying to understand how well your body is utilizing T3 and how well you are converting T4 into T3

Today, I want to walk you through why the total T3 thyroid lab test is so important, what information it provides, and, hopefully, convince you to get it tested the next time you get your thyroid labs drawn. 

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.  

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What Exactly is Total T3?

Before we jump in let me provide some quick background information to set the stage for this discussion. 

If you’ve been around for a while then you know that all of my articles contain links to clinical studies which provide further information on the claims that I make. 

I’d like to do this in this article as well but, 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 why I believe that it has value to you as a thyroid patient. 

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 thyroid patients in the past.  

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. 

Total T3 (1) should be differentiated from Free T3 (2) as they both provide different but useful information. 

Thyroid patients should care a lot about T3 for one important reason: 

The more T3 available to your body, the better you will feel. 

This simple logic is why it’s so important to test your free thyroid hormones (free T3 and free T4) in addition to the standard thyroid lab tests such as the TSH

Total T3 and free T3, are perhaps the most important of all thyroid tests that you can order because they give you the most information valuable information. 

They help you understand how well your thyroid gland is working, how well your body is converting T4 to T3, and whether or not that hormone is getting to your cells. 

In addition, most of the low thyroid symptoms that thyroid patients experience can directly be blamed on low T3 (this isn’t universal but tends to be true for most people). 

If this information is all new to you then make sure you check out this article which walks you through all 10 thyroid lab tests, what they mean, and why you need them. 

Free T3 vs Total T3

A lot of thyroid patients get confused when talking about these two tests so let’s set the record straight. 

Free T3 is a measure of the free and active T3 (3) thyroid hormone floating around in your bloodstream. 

Total T3, on the other hand, is a measure of both the free and active T3 as well as the bound and inactive T3 floating around in your bloodstream. 

Because of this, total T3 is a larger and broader measurement of T3 and the values should be much higher when comparing it to free T3. 

This may sound confusing until you learn why the body has two different ways of moving T3 around. 

Because T3 is so powerful (4), your body only wants to have a small amount of it active at any given time. 

The rest of the T3 floating around in your body is bound up to a protein so that it can be transported to other cells and tissues without interfering with other organs along the way. 

The unbound and active T3 is known as free T3 and this is the measure that you get when you test free T3. 

This free T3 is ready to be used by the body and your cells at a moment’s notice. 

As a percentage of all T3, free T3 is less than 1% of all of the T3 in your bloodstream. 

The bound and inactive T3 is known as total T3 and this is the measure that you get when you test total T3. 

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

As a percentage of all T3, this measurement accounts for 99% of T3 in your bloodstream (5) which is why this value is much larger when compared to free T3. 

Most doctors are far more concerned with the active portion, though, because that’s really what your body uses. 

For this reason, free T3 is often ordered more frequently than total T3. 

But that doesn’t mean that total T3 has no value. 

In fact, the opposite is true. 

Total T3 provides a bigger picture as to what is happening with T3 in your body. 

It helps provide answers to questions such as these: 

From a practical standpoint, what do the values of free T3 and total T3 mean for you as a thyroid patient? 

I like to think of it like this:

Free T3 gives you a measurement of the short-term availability of T3 in your system. 

In other words, free T3 is a better measurement of your T3 levels at any given point in time. 

Total T3, on the other hand, provides you with a more stable and long-term picture of T3 in your system. 

You may see higher day-to-day fluctuations when testing free T3 but these fluctuations should be ironed out when looking at total T3. 

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To help drive this point home, consider this example:

Imagine you are someone taking a thyroid medication that contains T3 like Armour thyroid

Now imagine you go in to get your thyroid labs checked and your free T3 value comes back as low normal. 

From here, you have to make a choice: 

Do you increase your dose of Armour thyroid? Do you add T3 thyroid medication to your Armour? Do you drop your dose of T4?

It’s hard to know which is the right answer without more information. 

And this is where total T3 steps in:

If you test your total T3 and find that it comes back as high normal then you know that you don’t need to adjust your dose of Armour thyroid upward. 

In other words, the free T3 level was just a day-to-day variation and not much stock should be placed on it. 

On the other hand, if you test your total T3 and find that it comes back as low normal then you know the free T3 lab test wasn’t just a day-to-day variation and you can consider increasing your dose. 

This is just one practical example of how testing your total T3 can help drive your treatment in the right direction. 

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 its primary value comes from being a precursor hormone for the production of T3. 

Most of the T3 floating around in your body is created by converting it directly from the stores of T4 that your thyroid gland produces (6). 

Put another way:

T4 has a lot of potential value because it can be converted into T3 as necessary. 

Doctors know this potential which is why they make the assumption that if your body has enough T4 that it will automatically produce the required amount of T3 that it needs. 

In other words, they are trying to take a step back and let your body naturally determine how much T3 it needs on its own. 

Logically, this makes sense. 

Unfortunately, it doesn’t play out this way in the real world. 

In the real world, we find that the thyroid conversion process can be influenced negatively by many different variables (7). 

If these negative variables are present then you can give a thyroid patient all of the T4 in the world but they won’t be able to convert it or activate it. 

And this is exactly what happens to many thyroid patients who are taking thyroid medications like levothyroxine. 

As a quick overview, here are some of the variables that can negatively impact T4 to T3 conversion: 

If you have any of these conditions then the T4 that you are taking in the form of thyroid medication may never actually turn into T3. 

For this reason, you always want to look at both free T3 and free T4 (as well as total T3) together. 

Even though this is true, and it is a problem for many thyroid patients, free T4 as a thyroid lab test is still valuable. 

Just like free T3, 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. 

Knowing how much free T4 is in your body is valuable because it helps you understand how much potential T3 your body can create. 

When it comes to biological activity, T4 still has some activity (11) but is far less active than T3. 

Reference Ranges for Total T3 & What They Mean

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

First off:

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

Each lab creates its 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. 

Secondly:

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 total T3 is usually around 76 to 181 ng/dL. 

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

This example highlights someone who has an obviously low total T3. 

This patient has a total T3 of 75 ng/dL which is below the range of 76 ng/dL to 181 ng/dL. 

This one is obvious and easy to identify because it falls outside of the normal reference range. 

In cases such as these, you will want to put a priority on increasing total T3 by whatever means necessary. 

This might mean taking a thyroid medication with T3, increasing your dose of T3, or taking supplements to help support T3 levels. 

Example of a low-normal Total T3: 

Perhaps a more common scenario that thyroid patients will run into is that of a low normal total T3. 

A low normal total T3 is one that falls inside of the standard reference range but is on the low end of that range. 

This example illustrates this concept perfectly. 

This patient has a total T3 of 91 ng/dL with the same range of 76 ng/dL to 181 ng/dL. 

Even though the result of 91 ng/dL falls inside of the range, it’s on the lower end. 

This patient is someone who is able to produce enough T3 to stay inside of the range but not enough to be optimal. 

And those patients who are suboptimal often continue to experience low thyroid symptoms like fatigue, weight gain, constipation, cold intolerance, hair loss, and so on. 

Much like the previous example, treatment here would focus on improving that total T3 with the use of T3-containing thyroid medications or T3 support supplements

Example of an “optimal” Total T3: 

Now let’s look at someone who has a total T3 in the optimal range:

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 just like this patient. 

Their result is 171 ng/dL which is very close to the high end of the range at 181 ng/dL. 

And this isn’t just my opinion, by the way. 

We know from some studies that higher baseline levels of T3 are associated with more weight loss (12) and better management of low thyroid symptoms. 

If you are paying attention then you will probably notice that this patient also has a slightly elevated free T3 which is being flagged as high. 

Some doctors, if they were to see this, might try to convince the patient that they need to lower their dose or that they are hyperthyroid. 

While it is possible that you can become hyperthyroid with an elevated free T3, you shouldn’t automatically make that assumption based on one lab test. 

This is why you always need to order the total T3. 

The total T3, in this example, is telling you that the patient has a steady long-term optimal T3 level. 

The free T3, which fluctuates day to day, can be high today but perhaps it may be normal or high normal tomorrow. 

You wouldn’t want to make a decision based only on the free T3. 

In a perfect world, you would be able to optimize your free T3 and total T3 without suppressing your TSH (which is possible). 

Example of a high Total T3: 

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 such and you will often experience some set of symptoms consistent with hyperthyroidism (anxiety, heart palpitations, weight loss, hair loss, tremors, diarrhea, etc.). 

You can sometimes get away with a high free T3 for the reasons listed above but you really want to avoid having a high sustained total T3 for long periods of time.  

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, treatments, and medications which help you maintain a high normal total T3 in the optimal range. 

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. 

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 just getting older). 

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, as well as 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 should get a complete thyroid lab test which includes the total T3. 

The total T3 test may not be necessary each and every time that you check the status of your thyroid with lab tests but they should be required for your initial evaluation (or if you’ve never had it tested before). 

Final Thoughts

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

This is especially true for those people who are taking thyroid medication faithfully but remain symptomatic. 

The total T3 lab test is a broad measurement of both active and bound T3 in your body. 

Total T3 should be differentiated from free T3 and free T4 as they all provide different information. 

When possible, do your best to optimize your total T3 to the top 30% of the reference range while maintaining a non-suppressed TSH. 

Following these rules will help you manage your thyroid while avoiding potential risks of hyperthyroidism.

Now I want to hear from you:

Have you had your total T3 tested? If so, what were your levels?

Is your total T3 optimal?

If not, are you planning on doing anything to help increase its value?

How are you feeling in relation to your total T3 lab test?

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

Leave your questions, comments, or experience below! 

#1. https://www.labcorp.com/tests/002188/triiodothyronine-t-sub-3-sub

#2. https://www.labcorp.com/tests/010389/triiodothyronine-t-sub-3-sub-free

#3. https://www.ncbi.nlm.nih.gov/pubmed/2673754

#4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3433956/

#5. https://www.ncbi.nlm.nih.gov/pubmed/7749500

#6. https://www.ncbi.nlm.nih.gov/pubmed/12915350

#7. https://www.ncbi.nlm.nih.gov/pubmed/27051079

#8. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3148770/

#9. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5461198/

#10. https://pubmed.ncbi.nlm.nih.gov/8157857/

#11. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4699302/

#12. https://www.ncbi.nlm.nih.gov/pubmed/28138133

why the total t3 thyroid lab test is so important

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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 80,000+ people have used them over the last 6 years. You can read more about my own personal health journey and why I am so passionate about what I do.

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