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, thyroid test results, and thyroid medication. That’s why I discuss them in-depth in my book, “The Thyroid Connection.”

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. This can help you and your doctor ensure you enjoy the benefits of optimal thyroid levels.

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Types of Thyroid Hormone Tests & Optimal Thyroid Levels

Many doctors who suspect a patient has something wrong with their thyroid only check their Thyroid Stimulating Hormone (TSH) test levels, which indicates 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 thyroid tests results 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 blood 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 test level is high in your thyroid test results, this can be a sign that you are under-producing thyroid hormones and you are hypothyroid.
  • If your TSH test level is low in your thyroid test results, 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.

Normal vs Optimal Thyroid Levels

If your thyroid test results indicate “normal” TSH test levels– i.e. your TSH falls within the normal reference range used by most conventional doctors and recognized by the American Thyroid Association — 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” TSH test levels in your thyroid test results, then you may have thyroid dysfunction, such as subclinical hypothyroidism.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.

Free T4 Thyroid Test Result

  • If your Free T4 level is high in your thyroid test results, it can indicate an overactive thyroid or hyperthyroidism. 
  • If your Free T4 is low in your thyroid test results, it can indicate an under-active thyroid or central 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.3

Free T3 Thyroid Test Result

  • If your Free T3 level is high in your thyroid test results, it indicates that your thyroid is overactive or hyperthyroidism.
  • If your Free T3 is low in your thyroid test results, 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 in thyroid test results. 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.4

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 disorder 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. These thyroid antibodies 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.
Interpreting Your Thyroid Lab Test Results – Infographic – Amy Myers MD®Interpreting Your Thyroid Lab Test Results - Infographic - Amy Myers MD® Your Thyroid Lab Test Results – Infographic – Amy Myers MD®

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 of thyroid test results alone don’t tell the whole story. I recommend ordering the following tests to get a complete picture of a patient’s thyroid problems and health.

  • TSH 
  • 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 function test panel, they’re usually relying on “normal” thyroid test results 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 for thyroid test results become more narrow. Yet still today, most doctors and laboratories haven’t updated their practices for optimal thyroid levels.

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.5

 I believe the most optimal thyroid levels are:

  • 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 thyroid levels reference ranges while working with you to restore your optimal thyroid levels. However, if that is not the case, I recommend using a lab company such as My Labs for Life so that you can easily order a complete thyroid panel and take your results back to your physician to have them reviewed.

The Myers Way® to Support Thyroid Health

The Myers Way® Multivitamin is tailor-made to help support optimal thyroid levels. I personally lived with thyroid issues. I’ve spent my career perfecting the art of supporting thyroid health for myself, the patients in my clinic, and, now, anyone who wants to support healthy thyroid and adrenal function. I custom-formulated this multi to be the perfect multivitamin for virtually everyone. However, I created it for those with thyroid dysfunction in mind. In fact, all of my patients with hypo- or hyperthyroidism, including Hashimoto’s and Graves’ disease, had my daily multivitamin in their treatment plans.

This specially-formulated multi is jam-packed with micronutrients in the forms your body wants and the amounts your thyroid needs. With optimal levels of thyroid-supporting minerals such as zinc, selenium, and iodine, alongside antioxidants including vitamins C and E and other free radical scavengers, no other multivitamin on the market does more to support your thyroid!

For more information, check out my interview with Mary Shomon on the importance of thorough thyroid testing and diagnostics.


Article Sources

  1. Physiology of the Hypothalamic-Pituitary-Thyroid Axis. Stefano Mariotti, Paolo Beck-Peccoz. NCBI. 2016.
  2. High and low TSH Levels: What They Mean. Mary Shomon. Very Well Health. 2019.
  3. What to Know About T3 Levels. Aaron Kandola. Medical News Today. 2020.
  4. Overview of Reverse T3 Thyroid Hormone. Mary Shomon. Very Well Health . 2020.
  5. Interpreting Thyroid Levels Tests. Corey Whelan. Healthline. 2019.