Optimal Thyroid Levels

One of the questions I am most frequently asked is, “what are the most important thyroid function tests to check to assess your thyroid’s function?” The appropriate tests, along with what your thyroid lab results really mean, are two of the essential topics to understand to determine if you genuinely 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 these two topics. That’s why I discuss them in-depth in my New York Times bestseller, The Thyroid Connection.

In this article, I’ll explain what each thyroid blood test measures, why your doctor should check them, and what the optimal reference ranges are to ensure your thyroid is functioning optimally.

TSH – Thyroid Stimulating Hormone

The hypothalamus, which is responsible for managing hunger, thirst, sleep, hormones, and body temperature, among other vital functions, continuously monitors the level of thyroid hormones present in your bloodstream. 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 Thyroid Stimulating Hormone, which is sent directly to the thyroid to produce more thyroid hormone, or T4.

As a result, your TSH level is actually an indication of what your pituitary is doing based on your hypothalamus’ feedback loop, rather than how your thyroid gland is functioning. Because of this negative feedback loop, the meaning of the results is often counterintuitive and confusing.

• If TSH is high – this can be a sign that you are under-producing thyroid hormones and you are hypothyroid

• If TSH is low – this can be a sign that you are over-producing thyroid hormones and are hyperthyroid, or that you are on too much supplemental thyroid hormone. Supplemental T3 or natural desiccated thyroid hormone with T3 can artificially suppress your TSH, so in the absence of symptoms, it could be perfectly normal.

• If your TSH is ‘normal’ – i.e. your TSH falls within the normal reference range, this could indicate that you do not have thyroid dysfunction. However, as I write in my book, “normal” and “optimal” levels have two very different meanings. So, if you still have symptoms and are in the “normal” — not “optimal” — range then you likely could have thyroid dysfunction

T4 – The Storage Form of Thyroid Hormone

Once TSH signals to 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 is circulated throughout the bloodstream and stored in tissues so that it’s available when needed. I liked to measure Free T4 (FT4) since it is unbound and able to act in the body.

• If FT4 is high – it can indicate an overactive thyroid or hyperthyroidism

• If FT4 is low – it can indicate an underactive thyroid or hypothyroidism

Free T3 – 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. I like to think of them as the gas.

• If FT3 is high – indicates that your thyroid is overactive or hyperthyroidism

• If FT3 is low – you may not be converting T4 to FT3 very well and you could have hypothyroid symptoms even if your TSH and FT4 are within range. This is one of the most common causes of low thyroid or hypothyroidism I saw in my practice.

Reverse T3 – The Brakes

Your body also uses a portion of the T4 to create Reverse T3 (RT3), another inactive form of thyroid hormone. RT3 can attach to the receptors for Free T3 to slow down your metabolic processes. For that reason, I call RT3 the brakes.

• 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 the RT3/FT3 ratio. I like that to be less than a 10:1 ratio.

Thyroid Antibodies – Your Immune System’s Attack on Your Thyroid

The vast majority of thyroid conditions are autoimmune, which means your immune system is attacking your thyroid. The hypothyroid form of autoimmune thyroid is Hashimoto’s. 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, the symptoms of 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 and 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 are typically elevated in Hashimoto’s patients.

• If your antibodies are elevated – your immune system is attacking your thyroid and you have autoimmune thyroid disease, or you are on the autoimmune spectrum.

What Thyroid Levels Your Doctor Should Check

Most conventional medicine doctors only check your Thyroid Stimulating Hormone (TSH) levels. If you are lucky, they will test your Free T4 levels to see if you are low on the storage form of thyroid hormones. However, as we’ve just covered, there are many factors involved in optimal thyroid function, so those two levels alone don’t tell the whole story. To get a complete picture of a patient’s thyroid health and medication needs, I recommend ordering all of the thyroid tests listed below.

• TSH

• Free T4

• Free T3

• Reverse T3

• Thyroid Peroxidase Antibodies (TPOAb)

• Thyroglobulin Antibodies (TgAb)

The Optimal Thyroid Lab Ranges Your Doctor Should Use

Even if your doctor does order a complete thyroid panel, they’re usually relying on “normal” reference ranges. Unfortunately, these are too broad and often inaccurate. When they created the lab reference ranges for a healthy thyroid, they later discovered that they had included people who already had thyroid dysfunction!

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 definition of what constitutes a thyroid problem.

In my functional medicine practice, I have found that the ranges below are the ones in which my patients (and myself) thrive. I listen to my patients as well and take how they are feeling into account.

• TSH 1-2 UIU/ML or lower (Armour or compounded T3 can artificially suppress TSH)

• FT4 >1.1 NG/DL

• FT3 > 3.2 PG/ML

• RT3 less than a 10:1 ratio RT3:FT3

• TPO – TgAb – < 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. Then, that she or he will 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 here, go to a lab for a blood sample, and take your test results back to your physician or a dietitian to have them reviewed.

My book, The Thyroid Connection, is an additional resource to help you discover why your doctor might have your thyroid diagnosis and treatment wrong. I also discuss how to work with your doctor to get the correct diagnosis, which blood tests to request, and what each test means.

It also describes the roles of gut health, diet, toxins, infection, and stress in thyroid dysfunction, and provides a step-by-step, 28-day plan to help you jumpstart your thyroid health. Most importantly, The Thyroid Connection will help you take back your life and regain your vitality.

Amy Myers, MD

Amy Myers, MD is a two-time New York Times bestselling author and an internationally acclaimed functional medicine physician. Dr. Myers specializes in empowering those with autoimmune, thyroid, and digestive issues to reverse their conditions and take back their health. In addition, she is a wife, mother, and the successful founder and CEO of Amy Myers MD®.