One question I am most frequently asked is, “What are the most important thyroid tests to check to assess my thyroid’s function?” This, along with what the thyroid test results mean, are two of the most important topics to understand to determine if you truly have thyroid dysfunction or not. And let me tell you, there is a lot of misinformation on the internet and in the conventional medicine world surrounding thyroid tests and thyroid test results. That’s why I discuss them in-depth in my book, “The Thyroid Connection.”
In this article, I’ll explain what each thyroid test measures as well as how to interpret your thyroid test results. I’ll also discuss why your doctor should carefully review your thyroid test results, and what the optimal reference ranges for thyroid test results are to ensure your thyroid is functioning at its best.
Types of Thyroid Tests & Optimal Thyroid Hormone Levels
Many doctors who suspect a patient has something wrong with their thyroid only check their Thyroid Stimulating Hormone (TSH) levels, which indicate if the patient has hypo- or hyperthyroidism. If they’re lucky, a doctor will test their Free T4 levels to see if they are low on the storage form of thyroid hormones. While these tests do a great job to uncover the nature of a patient’s disease, they only tell you a small part of the story.
To get a complete picture of a patient’s thyroid health and medical needs, I recommend a doctor order all six tests listed below.
What is TSH, or Thyroid Stimulating Hormone?
The hypothalamus is responsible for managing hunger, thirst, sleep, hormones, and body temperature (among other important functions). It also continuously monitors the level of thyroid hormones present in your bloodstream.1 If it determines that energy levels are low, it sends out TRH, Thyroid Releasing Hormone, to your pituitary gland.
Your pituitary gland then releases TSH, or Thyroid Stimulating Hormone. TSH is sent directly to your thyroid to produce more T4, the storage form of thyroid hormone. Your TSH level is an indication of what your pituitary gland is doing based on your hypothalamus’ feedback loop, rather than how your thyroid is actually functioning. This misunderstanding of thyroid test results by conventional medicine doctors often leads to counterintuitive patient advice.
TSH Thyroid Test Result
- If your TSH level is high, this can be a sign that you are under-producing thyroid hormones and you are hypothyroid.
- If your TSH level is low, this can be a sign that you are over-producing thyroid hormones and are hyperthyroid. It could also mean you are on too much supplemental thyroid hormone. Supplemental T3 or natural desiccated thyroid hormone with T3 can artificially suppress your TSH levels. So, in the absence of symptoms, it could be perfectly fine if the level appears low.
If your TSH level is “normal”– i.e. your TSH falls within the normal reference range used by most conventional doctors — it could indicate that you do not have thyroid dysfunction. However, as I write in my book, “normal” and “optimal” levels mean very different things. If you still have symptoms and are in the “normal” range rather than “optimal,” then you may have thyroid dysfunction.2
What is T4, or the Storage Form of Thyroid Hormone?
Once TSH signals your thyroid to ramp up the production of its hormones, it produces the four different types of thyroid hormone: T1, T2, T3, and T4. The primary output of your thyroid is T4, which is a storage form of the hormone. It circulates throughout the bloodstream and stays in the tissues so that it’s available when needed. I like to measure Free T4 (FT4) since it is unbound and able to act in the body.3
Free T4 Thyroid Test Result
- If your Free T4 level is high, it can indicate an overactive thyroid or hyperthyroidism.
- If your Free T4 is low, it can indicate an underactive thyroid or hypothyroidism.
What is Free T3, or “the Gas”?
When each local area of your body determines that it needs more power, it converts storage T4 into Free T3, which is the active form of the hormone. These hormones attach to receptors inside of your cells to power your metabolic processes, which is why I like to think of them as the gas.4
Free T3 Thyroid Test Result
- If your Free T3 level is high, it indicates that your thyroid is overactive or hyperthyroidism.
- If your Free T3 is low, you may not be converting T4 to Free T3 very well and you could have hypothyroid symptoms even if your TSH level and Free T4 level are within the “normal” range. This is one of the most common causes of low thyroid or hypothyroidism that I saw in my clinic.
What is Reverse T3, or “the Brakes”?
Your body also uses a portion of the T4 to create Reverse T3 (RT3), another inactive form of thyroid hormone. This one can attach to the receptors for Free T3 in order to slow down your metabolic processes. For that reason, I call RT3 the brakes.5
Reverse T3 Thyroid Test Result
- If RT3 is high – you are likely converting too much T4 to RT3 and not enough to FT3, which can cause hypothyroid symptoms even if your TSH and T4 levels are optimal.
- In addition, I look at something called an RT3:FT3 ratio. I like that to be less than a 10:1 ratio.
What are Thyroid Antibodies?
The vast majority of thyroid conditions are autoimmune, which means your immune system is attacking your thyroid. The hypothyroid form of autoimmune thyroid disease is Hashimoto’s, and the hyperthyroid form (which is what I had) is Graves’ disease. It’s incredibly important to know if your thyroid condition is autoimmune because once you develop one autoimmune disease, you’re three times as likely to develop another.
It’s also important because, as I explain in both of my books, The Thyroid Connection, and The Autoimmune Solution, autoimmune disease can be reversed by addressing its root causes: leaky gut, diet, toxins, infections, and stress.
There are two main types of thyroid antibodies. Thyroid peroxidase antibodies (TPOAb) attack an enzyme used to synthesize thyroid hormones. TPOAb are commonly elevated in both Hashimoto’s and Graves’ disease patients. Thyroglobulin Antibodies (TgAb), attack thyroglobulin, which your thyroid uses to produce its hormones. They are typically elevated in Hashimoto’s patients.
Thyroid Antibodies Test Result
- If your antibodies are elevated, your immune system is attacking your thyroid, and you either have autoimmune thyroid disease, or you are on the autoimmune spectrum.
What Thyroid Tests Should Your Doctor Order?
Most conventional medicine doctors only check your Thyroid Stimulating Hormone (TSH) levels and Free T4 levels to see if you are low on the storage form of thyroid hormones. However, as we’ve just covered, optimal thyroid function involves many factors. Those two levels alone don’t tell the whole story. I recommend ordering the following tests to get a complete picture of a patient’s thyroid health.
- Free T4
- Free T3
- Reverse T3
- Thyroid Peroxidase Antibodies (TPOAb)
- Thyroglobulin Antibodies (TgAb)
The Optimal Thyroid Levels
Even if your doctor does order a complete thyroid panel, they’re usually relying on “normal” reference ranges that are too broad and often inaccurate. When lab reference ranges for a healthy thyroid were created, it was later discovered that people who already had thyroid dysfunction were included in those ranges!
Because of this, in 2003, the American Association of Clinical Endocrinologists recommended that the lab reference ranges become more narrow. Yet still today, most doctors and laboratories haven’t updated their practices.
In my clinic, I found that the ranges below are where my patients (and myself) thrived, not just lived! I listened to my patients and took how they were feeling into account as well.6
- TSH levels of 1-2 UIU/ML or lower (Armour or compounded T3 can artificially suppress TSH)
- FT4 levels >1.1 NG/DL
- FT3 levels > 3.2 PG/ML
- RT3 levels < 10:1 ratio RT3:FT3
- TPO – TgAb levels < 4 IU/ML or negative
If Your Doctor Won’t Order a Full Thyroid Panel for You
My sincere hope is that your doctor is willing to order all of the labs listed above and then use the optimal reference ranges while working with you to restore your thyroid function. However, if that is not the case, I have partnered with a lab company called My Labs for Life so that you can easily order your own lab tests online. You can order a complete thyroid panel and take your results back to your physician to have them reviewed.