Thyroid Laboratory Testing

Thyroid Laboratory Testing

Thyroid Laboratory Testing 

In last week’s blog I discussed a basic overview of thyroid health: what the thyroid is, what it does, and what some causes and symptoms of hypothyroidism might be. (You can check that out here!). Now let’s dive into thyroid laboratory testing as this is one of the places functional medicine absolutely shines. 

When seeing a conventional primary care provider and even an endocrinologist they will often check your thyroid status by testing a TSH (thyroid stimulating hormone) and maybe a T4 (thyroxine), but that doesn’t give us the whole picture. In Functional Medicine, we want to see these levels in addition to a few others to see how our bodies are utilizing the hormones (or not) in relation to symptoms. Below is a list of thyroid labs and what they mean and as you’ll see, knowing all your numbers gives a better picture of the whole puzzle. 

  • TSH (Thyroid Stimulating Hormone): TSH is the hormone signal sent from the pituitary gland to the thyroid and tells the thyroid how much thyroid hormone to make and release. This is often the first test and it is a good initial screen tool to test thyroid function. Changes in TSH are often an early warning sign. A high TSH indicates that the thyroid is not making enough thyroid hormone (ie: hypothyroidism)
  • Total T4 (thyroxine): Total T4 is the total amount of free and bound T4 if the blood. T4 is the main thyroid hormone circulating in the blood, and this accounts for about 90% of the thyroid hormone circulating in the body. 
  • Free T4 (thyroxine):. Free T4 is the amount of T4 that is available for use in the body, whereas total T4 is bound and free hormone. T4 is converted into the active thyroid hormone T3 or less active form reverse T3.
  • T3 numbers: T3 is responsible for entering the cell’s nucleus and responsible for all of the downstream effects of thyroid hormone in the many organ systems.
  • Free T3 (Triiodothyronine ): T4 is converted to T3 peripherally and often referred to as the “gas pedal” meaning it helps with metabolism and thyorid function. T3 competes with reverse T3 for cell receptor sites and we often see an imbalance here. 
  • Reverse T3: RT3 is the less active T3 form and often is referred to as “putting on the brakes.” High levels of reverse T3 are often seen in hypothyroidism and contribute to many of the symptoms we see with hypothyroidism. Reverse T3 competes for cell receptor sites with free T3. When Reverse T3 is high it is not so much a problem with the thyroid but some other systemic issue like stress, inflammation, infection, nutrient deficiencies, etc… I often see reverse T3 being too high and free T3 being too low in patients who are busy moms, entrepreneurs or athletes – often driven by stress
  • TPO Antibodies and Anti-TG antibodies: thyroid antibodies indicate there is an underlying autoimmune disease going on, such as Hashimoto’s. Hashimoto’s and high antibodies can be seen with a normal TSH and may be an early indicator that thyroid dysfunction is coming. 

Some thoughts on thyroid laboratory Testing…

As you can see, making treatment decisions based on TSH alone is not as helpful as looking at the whole picture and along those same lines, we also know for thyroid health, “normal” is not always optimal. For example, in my experience as a thyroid patient, I feel best when my TSH is between 1 and 2 and there have been times when it has been up in the 4+ range and I felt awful yet, back then my conventional primary care team told me it was normal and made no adjustments or dug any deeper. This is something I often hear from patients. 

It is also not common to routinely test for thyroid antibodies, but don’t we want to know if someone has an autoimmune disorder? In conventional medicine, the answer is: no. This doesn’t change their treatment so why would they need to know this? In functional medicine, we believe in the reversal or slowing of autoimmune disease by utilizing lifestyle medicine, supplementation and medications and trying to figure out the root cause and potentially reverse the disease. 

Normal vs. Optimal Lab Values

You’ve heard me say it before but normal labs within the reference ranges are NOT always optimal and when it comes to thyroid labs, this is often the case. See the thyroid laboratory testing numbers below to see how normal differs from what we consider optimal for thyroid and overall health.


Reference Range



0.4-4.50 mIU/L


Free T4

0.8-1.8 ng/dl

1-1.5 ng/dl

Free T3

2.3-4.2 pg/ml

3.2-4.5 pg/ml

Total T3

76-181 ng/dl

120-181 ng/dl

Reverse T3

11-31 ng/dl

11-18 ng/dl

TPO antibodies

0-34 IU/ml

No optimal range

TG antibodies

0-40 IU/ml

No optimal range

The good news is, you are not destined for a life of just medication and feeling mediocre. Medications may be necessary if thyroid disease is more advanced but some patients are able to fix underlying causes and get off of or decrease their dose of medications significantly. And while getting off of medications might be the goal for some, the real goal is getting the thyroid functioning better and more importantly improving symptoms, and sometimes medication is a piece to that.

If you are looking for someone to work on or investigate your thyroid health, I am your gal! Book a free 15 minute introduction call below to charge of your health and feel better!