Testing for Thyroid Conversion Issues (Check These Lab Tests)

Testing for Thyroid Conversion Issues (Check These Lab Tests)

What is Thyroid Conversion?

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Thyroid conversion is probably one of the most important aspects of thyroid function that you probably aren’t even aware of. 

That’s a bold statement, I know, but I think you’ll agree with me after we have this discussion. 

First off:

What is thyroid conversion? 

Thyroid conversion is the process by which your body ACTIVATES the thyroid hormone that it produces. 

Why is this important?

Well, roughly 80% of the T3 that is in your body is produced via this activation process. 

Which means…

If you are not properly converting or activating thyroid hormone in your body, you may be losing out on the MAJORITY of T3 that your body is capable of producing. 

Let’s break this down to make it a little easier to digest with some important facts:

Fact #1. T3 thyroid hormone is by far the single most important thyroid hormone in your body. It is roughly 300 times more biologically active (1) than T4 thyroid hormone. 

Fact #2. Most thyroid hormone produced by your body is NOT T3 but is actually T4. 

Fact #3. Only 20% of T3 in your body (2) is directly produced by the thyroid gland. 

Fact #4. Roughly 80% of T3 is created through peripheral thyroid conversion in various tissues in your body. 

Fact #5. Doctors know that this conversion process occurs and is important but pay NO attention to the process as they assume that it is always occurring. 

Fact #6. There are several KNOWN issues that slow down or inhibit this conversion process including genetic factors that are outside of your control. 

Notice here that I have stated these things as FACTS and not as opinions. 


Because these facts are verified through physiological studies. 

And physiology is another way of describing how systems in the body function. 

Physiology, for the most part, is not up for debate. 

What is up for debate is how these things impact you clinically (meaning how they affect your symptoms). 

And that’s exactly what we are going to be talking about today. 

After reading this article you should gain an appreciation for the important role that this thyroid conversion proce​​ss plays and how exactly to test to see if it is working properly. 


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How do you test for it?

Is it possible to test for thyroid conversion issues?

Yes, it’s actually quite easy. 

Why haven’t you heard about it before then?

Because your doctor has probably only ever ordered tests such as the TSH (thyroid stimulating hormone) and free T4

And these tests do NOT give you enough information to reliably assess whether the conversion process is working. 

This puts you as a patient in somewhat of a bind!

The only way to determine your conversion status is to order the ​​right tests and the only way to get those tests is through your doctor (well, that’s not entirely true as there are some ways to order your own labs). 

Even if you can get your doctor to order these tests, though, it will still be up to you to interpret the results. 


Because doctors are not accustomed to ordering these tests and don’t really understand their significance or their importance. 

But don’t worry, it’s actually not that hard to understand the conversion process and we will explain that more below. 

What you need to know right now is that in order to test your conversion status you need AT LEAST the following thyroid lab tests:

*Indicates that these tests are helpful but not absolutely required. 

I have detailed information on each of these lab tests and you can look at them individually but here I am going to take a look at these tests in specific patterns which can indicate conversion issues. 

Patterns that indicate low thyroid conversion

When testing for thyroid conversion issues you really need to make sure that you are looking at the entire picture. 

This ‘entire picture’ includes both your lab tests and how you are feeling. 

Why is this important?

Because not all lab tests are 100% accurate, and this includes thyroid lab tests. 

So it’s possible for you to have abnormal results which may not be important if you are feeling 100% normal.

So don’t base any decisions that you may have on abnormal lab tests in the event that you are already feeling fine. 

But the chances of you reading this and feeling fine are slim (why would you read it if you were?) so I am assuming that this isn’t the case. 

By the way, when I talk about whether your tests are “high”, “low”, or “normal” I am referring to the ranges found within this blog post

If the concept of an optimized high, low, and normal reference for your thyroid lab tests is new to you be sure to read that article BEFORE reading this one! 

So, when evaluating for conversion issues look for these thyroid lab patterns:

#1. High-free T4 and low-free T3

The first and probably most obvious way to diagnose thyroid conversion issues is by looking at your free T4 and free T3. 

We know from physiology that your body takes T4 and turns it into T3. 

So what do you think it would look like if there was a blockade which prevented your body from turning T4 into T3?

Well, you would expect to see a build-up of T4 like it was backed up behind a dam and you would expect to see low levels of T3. 

And that’s exactly what you see in thyroid lab tests if you have this type of thyroid conversion issue. 

This particular one is not rocket science and is incredibly easy to diagnose. 

But what type of people get this type of conversion problem?

Usually, people who have high-free T4 and low-free T3 are those people who are taking thyroid medication. 


Because most thyroid medications contain ONLY T4 thyroid hormone (medications like Synthroid and levothyroxine). 

So if you are pounding down levothyroxine and your body isn’t converting it you will see that your TSH will drop, your free T4 will increase, and your free T3 will drop or simply won’t increase. 

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In addition, you will also simultaneously find that you have all of the symptoms of hypothyroidism that are not going away despite getting treatment. 

And this is the situation that I think a great many of you are in right now. 

It stems from not ordering the right tests and from assuming (like your doctor is probably doing right now) that any T4 he/she gives you will be converted by your body to T3 without any issue. 

This is probably the easiest conversion problem to diagnose and the easiest to treat. 

#2. Low-free T4 and low-free T3

This pattern leads to a completely different type of conversion issue. 

There are many patients who are taking high doses of T4-only thyroid medication such as levothyroxine and Synthroid which are not being converted at a high enough rate for patients. 

This problem typically results in high-free T4 and low-free T3. 

But you can have another type of conversion issue which occurs simply because your body doesn’t have enough T4 thyroid hormone in circulation. 

If your free T4 levels are low then there simply won’t be enough substrate to draw from in order to create the free T3 that your body needs. 

So one problem is that of excess T4 resulting in low T3 and the other (this problem) is a problem of low free T4 which is simply not sufficient for your body. 

These low states of free T4 often occur in people who are either not getting enough thyroid medication (meaning their dose is too low) or in individuals who should be taking thyroid medication but who aren’t. 

People in the latter condition include people with untreated Hashimoto’s thyroiditis and early hypothyroidism or sub-clinical hypothyroidism

These people obviously NEED thyroid medication but they find that their TSH is in a normal-ish range so their doctor doesn’t feel the need to order further tests. 

The reality is that if they did order these tests they would find that their thyroid is struggling. 

I find this situation to be most common in early to mid-Hashimoto’s thyroiditis. 

Patients in this category have obvious thyroid damage but that damage isn’t yet reflected in their TSH. 

This is just one of many reasons why the TSH fails as the best test to identify low thyroid function if used by itself. 

#3. High reverse T3

This is probably the only test that you can look at in isolation to help determine if your conversion status is not working optimally. 

Reverse T3 is the anti-thyroid metabolite that your body produces when it can’t produce T3. 

Your body will take T4 and either turn it into T3 (good) or reverse T3 (bad if it’s in high amounts). 

So, it’s really like an all-or-nothing type of thing. 

You are either pushing your body to produce more T3 or you are pushing it to produce reverse T3. 

Does this mean that all people with conversion problems will have a high reverse T3 level?

Actually, no. 

This isn’t universally true but you will see it most of the time. 

But, for instance, if you have low free T3 and low free T4 (so there just isn’t enough to go around) then you will most likely see low/normal reverse T3. 

What type of people has high reverse T3?

Reverse T3 tends to rise in very specific scenarios and I have​​ a list of several that you can look at

One of the most important causes of elevated reverse T3 is calorie restriction or dieting (3). 

If you lose weight the unhealthy way then you will find that your reverse T3 will rise and your other thyroid lab tests will be relatively normal. 

But this elevation in reverse T3 is enough to indicate a thyroid problem by itself and it also indicates a problem with thyroid conversion. 

You should always test your reverse T3 when you are looking at thyroid conversion but don’t expect it to always be high!

#4. Low to normal TSH with symptoms of hypothyroidism

The three patterns mentioned above are the most common ways to identify thyroid conversion problems but I also want to include one more. 

This one is important because it may not be possible for many of you to get the tests that you need (free T3, reverse T3, and free T4). 

But just because you can’t get these tests doesn’t prevent you from making certain assumptions about your conversion status. 

Let’s imagine that you are someone who is currently taking thyroid medication (such as levothyroxine or Synthroid). 

Let’s also assume that you are taking enough thyroid medication that it has lowered your TSH to the point that your doctor is getting uncomfortable and doesn’t want to lower it any further. 

At this point, you could either have a lowish TSH or a normal TSH on the low end of normal

At this point, it’s possible to ASSUME that you have thyroid conversion problems if you fit this category AND if you also still have the symptoms of hypothyroidism. 

Symptoms such as weight gain, fatigue, hair loss, cold intolerance, depression, muscle aches, brain fog, and so on. 

If you have THESE symptoms and a lowish to low normal TSH then you can make the assumption that your body isn’t converting T4 into T3 without looking at free T3 and free T4 levels. 


Because we know that your body is getting enough T4 based on the fact that your TSH has dropped. 

And we also know that you wouldn’t be symptomatic in this situation UNLESS you also don’t have enough T3. 

Why? Because T3 is the thyroid hormone that helps you FEEL better. 

So even without the lab tests listed above, there are ways to make very educated guesses about your thyroid conversion status. 

Final Thoughts + Your Next Steps

We just spent a lot of time talking about how to properly diagnose thyroid conversion issues but what are you supposed to do if you find that you have them?

Treating conversion issues is usually as simple as focusing on things and therapies which help increase thyroid conversion and trying to reverse things that cause these problems. 

It usually looks something like this:

It’s often best to do ALL of these things at once as opposed to trying one and then going to the other after some period of time. 

The more therapies you layer on top of each other the quicker you will feel better and get back to your normal self. 

The first place to start, though, is always with your labs! 

But now I want to hear from you:

Are you someone who is struggling with thyroid conversion issues?

Have you been able to get the proper labs to determine if that is what is happening in your body?

If so, what did your labs look like?

Or are you struggling to get the right labs drawn?

Leave your questions or comments below to keep the conversation going!

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

#2. https://www.ncbi.nlm.nih.gov/books/NBK519566/

#3. https://www.ncbi.nlm.nih.gov/pubmed/12055988

testing for thyroid conversion problems

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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 7 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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