Before we dive into the answer to that question, please understand two things:
Getting the tests done is the first step. Utilizing the information is the next step. Different doctors use different ranges. A general practitioner (GP) may say, “This all looks normal.” Yet, a functional medicine doctor (FM) might say, “Wow, we’ve got stuff to work on here!”
There are some things to keep in mind about lab ranges:
|Lab Test||Conventional Range||Functional Range|
|TSH||0.5-5.5 uIU/mL||1.8 – 3.0 uIU/mL|
|Total T4||5.4 – 11.5 µg/dL||6-12 µg/dL|
|Total T3||60-181 ng/dL||100-180 ng/dL|
|Reverse T3||9.2 – 24.1 ng/dL||9.2 – 24.1 ng/dL|
|TPO Antibodies||>35 IU/mL||>35 IU/mL|
|TG Antibodies||>20 IU/mL||>20 IU/mL|
|Free T4||0.7 - 1.53 ng/DL||1.0-1.5 ng/dL|
|Free T3||2.3 – 4.2 pg/mL||3.0-4.0 pg/mL|
|TBG||15-30 µg/dL||18-27 µg/dL|
So you twist your doctor’s arm to order you all these tests that “some ‘Dr. Brooke’ from the Internet recommended.” Now what? The results need to be interpreted In our conventional medical model, issues that profoundly impact your thyroid—such as estrogen dominance, gut health and stress—aren’t addressed.
I see this over and over again. People manage to get this extensive list of tests from their regular doctor, but they aren’t really able to use that information to do the most important part: feel better. You’re told, “This all looks pretty normal.” And they’re right—for their model. But there’s more to the story, more to your story.
To get a better understanding of your story, your physiology, more is probably better. But that isn’t always possible due to insurance restraints, cost if out-of-pocket, and what your doctor deems as necessary.
Even among us functional medicine doctors, if you ask three different practitioners what their “minimum thyroid panel” is, you’ll probably get three totally different answers.
Rather than give you my exact list, let’s consider what we may be looking for and take into account: cost (if insurance isn’t footing the bill for expanded testing), your history, what medications you’re on, and what tests we’re going to be able to get (i.e. “If I can’t get that one, I’ll take this one” is a game I play a lot). Let’s also take into account what other issues you have that may be impacting your thyroid (like estrogen dominance).
But before we get into testing, let’s have a quick overview of thyroid physiology so that you have a framework to think about these tests:
It starts in your brain. TRH from the hypothalamus (which is typically not tested) stimulates your pituitary to release TSH. TSH is the signal to the enzyme TPO (thyroid peroxidase) in your thyroid to start making T4, and a bit of T3 (94% and 7% respectively).
At the thyroid, T4 is released and converted to T3, the metabolically-active form of thyroid hormone. This T4 to active T3 conversion occurs to about 60% of your T4. About 20% of it is converted to an inactive form called reverse T3. This is a protective mechanism to avoid overstimulation of your metabolism. The last 20% is converted to T3 forms called T3S (T3 Sulfate) and T3AC (T3 acetate). These two are also inactive forms but, they can be reactivated by healthy gut bacteria—one of many reasons a healthy gut is KEY to having enough thyroid hormone.
In the blood steam, hormones are mainly found bound to a protein carrier (in this case, mostly stuck to thyroid binding globulin or TBG). At some point, the hormone has to come off the carrier and become “free” T3 so it can bind to the internal, nuclear receptor of a cell and cause metabolic activation of that cell.
Now that you have a better understanding about the various hormones and their functions, here’s what we can glean from your blood work and when certain tests might be helpful:
If you are suspicious you have a thyroid problem, not yet on medication, or not sure if it’s even your thyroid at all, you’ll likely start with a TSH and Total T4, here’s why:
TSH is released from the pituitary (in response to TRH) and tells the thyroid gland to make and release T4. As your levels of T4 drop for whatever reason, that signals the pituitary to release more TSH to stimulate the thyroid to make more and more hormone (more T4). So what you see on labs when you are hypothyroid is an elevation in TSH, typically. This marker does move about a bit in some cases and there are special instances (i.e. a pituitary damaged by years of stress, Hashimoto’s) when you can be hypothyroid and have a normal or low TSH.
Total T4—both the free and the protein bound form of T4—is essentially the horsepower of your thyroid. Remember that most of the hormones are bound, which is why it is important to look at free levels as well. A low level indicates your thyroid isn’t able to make much hormone. When this level drops on labs, in conjunction with an elevation in TSH, you’ll be deemed “hypothyroid.”
These two tests together are the basic standard to rule in or out hypothyroidism by the technical definition (high TSH and low T4). However, this tells us nothing about T4-T3 conversion or a host of other thyroid problems you may have.
What’s more, this combo alone would not tell you why you are hypothyroid, i.e. due to autoimmune attack on the thyroid gland (known as Hashimoto’s), iodine deficiency (rare in the Western world), etc.
TP and TG Antibodies can be positive for many years before you become hypothyroid. Research shows that these antibodies with normal TSH and T4 are still predictors of future thyroid problems. And it’s also true that you can still feel like total crap when these are positive and your “thyroid labs are normal” because this immune system activation creates a ton of inflammation and symptoms such as brain fog, fatigue and joint pain. You can learn more about Hashimoto’s here.
This is why I recommend women get their antibodies tested every 6-12 months, and more frequently if they have unspecified hypothyroidism, have been pregnant, have PCOS or are going through peri-menopause. If these are positive, I not only have a why, but I can also work on the cause: the immune system.
Whether it’s Hashimoto’s or not, you can still have a lot of potential problems after T4 is released. The only way to find them is to utilize the tests for T3.
Here are those tests and in what situations you may want to consider ordering them:
This is the best way to see if you’re converting T4 into T3. This is warranted if you are taking thyroid medications and you still aren’t feeling great. You may be getting enough T4, but not converting it into active T3. This is also a good idea if your labs are normal but you still have hypothyroid symptoms including: fatigue, dry skin, constipation, difficulty losing weight, hair loss, brain fog, etc.
Remember, this is a loss of active T3 after conversion from T4 that we can’t get back, so we don’t want to lose too much down that pathway (about 20% goes here normally). This conversion to reverse T3 is sped up by cortisol and inflammation. So this is an important test if again, you have relatively normal looking labs but have a lot of hypothyroid symptoms, have normal T4 but low total T3, if you’re dealing with a lot of inflammation (from blood sugar imbalances, lack of sleep, poor diet, digestive issues, chronic injuries, etc.), or if you are under stress (remember stress comes from a lot of places you may not realize, click here for more on stress).
It’s always good to know how much Free T3 you have, because the moral of the thyroid physiology story is that it’s free T3 that ultimately binds inside your cells and increases the metabolic rate of that cell.
You can simply run a Free T3 test or you can infer how T3 is faring by a T3Uptake or TBG test (more on that below). Free T3 is a pricier test so if you’re paying cash one of the other two may be a good option.
A curious thing I’m seeing recently, with more providers getting hip to the necessity of evaluating T3, is this combo of tests: TSH, Total T4 and a Free T3. In this case, if the Free T3 is low we wouldn’t necessarily be able to tell why without also seeing Total T3. If Free T3 is low but total T3 was also low, then the problem is probably conversion and not an actual Free T3 issue.
What creates an actual problem with levels of Free T3 are estrogen and testosterone. Estrogen raises the amount of Thyroid Binding Globulin (the protein that carries around T3). When there’s more of the protein carrier, too much of your T3 is bound up leaving you with less free, less active T3 around. Testosterone does the opposite, it lowers TBG.
This sounds good right? More Free, active T3 around. Sadly, it’s not. When there’s too much free hormone around, your thyroid receptors (found everywhere in your body) get resistant, just like with insulin resistance: they stop heeding the thyroid hormone message. So either way, whether TBG is low or high, you can see low T3 symptoms.
So in lieu of a Free T3 test, you can look at levels of thyroid binding globulin (TBG is the test) or you can use a test called T3Uptake. This test has an inverse relationship with TBG, so when T3U is elevated you’ve got low TBG levels (often due to excess testosterone). Conversely, when T3U is low you’ve usually got an estrogen-related problem of too much TBG (thus too little Free T3). You may want to look at these binding globulin issues if you have any female hormone imbalances such as PCOS, if you take estrogen medications such as HRT or birth control, or if you have low thyroid symptoms but normal looking TSH and T4.
You don’t necessarily need all of these tests run all of the time, but if you aren’t sure what may be impacting your thyroid then it’s best to get a big-picture view and see what patterns present. This way you can know if your efforts are best spent working on stress, coming off the birth control pill, or healing your gut to quiet your immune system. While I strongly recommend you work with someone who can help you interpret your results, if your doctor won’t order these, you can get testing through services like Direct Labs. I welcome your questions at [email protected].
Sign up for this FREE 5-Day course and you'll learn how to:
It’s time to get the best results of your life — without feeling deprived of the foods you love — or exhausting yourself with exercise.
This free course includes videos, downloadable tools & resources, and podcast version so you can learn on the go.