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Thyroid Lab Tests & Understanding Your Results

When you understand the thyroid lab tests that are out there and which ones you should order, you'll save money, time, and - literally - blood by asking for the right tests and knowing what they mean.

We've talked about signs of a thyroid issue and why you should still be skeptical of your lab results if they come back as 'normal' while you're experiencing symptoms. Most importantly, we covered the difference between the conventional (wide) lab reference range vs. the functional (narrower) lab reference range. You want functional ranges - this is the range for optimal health.

In this article:

  1. Why your doctor might be ordering the wrong thyroid tests

  2. Which thyroid lab tests to ask for and what the results could mean

  3. How to order your own thyroid labs if your doctor won't work with you

  4. How often you should test your thyroid


Your doc could be ordering the wrong thyroid tests.

Ever thought about what it's like to go through med school? Even completing my training in functional medicine coaching & nutrition therapy was intense and there was a hoard of information to memorize.

That said, very few general physicians & family doctors can be specialists, though endocrinologists are somewhat better. Either way, if they're conventionally-trained, they may not be ordering you the lab tests you need to get a full picture of what's going on with your thyroid.

Many doctors will order a TSH and if you're lucky, T4 as well. That's not nearly enough to draw a conclusion about your thyroid health.

So which thyroid tests should you absolutely get?

These are the thyroid lab tests (blood) you should always get, in order to make sure you've got a good picture. Many labs/offices have a thyroid panel, but don't assume - make sure the panel includes each of these results and add on those that aren't included.

Below you'll also find a quick summary of what it means, roughly, to have a high, low, or normal result within functional ranges. This information is provided only for educational purposes, as I'm not a doctor. Thyroid labs tell a unique story in combination with each other, so you should always work with a qualified functional medicine doctor to determine what the collective group of your results means.

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TSH (Functional range: .9 - 2.0 IU/mL)

Short for Thyroid Stimulating Hormone. It is a signaling chemical created by the pituitary gland that tells the thyroid how much hormone to make. TSH is like the supervisor on an assembly line where the thyroid is the only worker: When your body needs more thyroid hormone so the supervisor (TSH elevates) yells louder, "make more hormone"! When your body has enough/too much thyroid hormone, the supervisor speaks softly or says nothing (TSH is normal or low), and less hormone is sent from the thyroid.

⬆️ TSH high: Thyroid is working overtime and the body is signaling for more active thyroid hormone. This can be a sign of hypothyroidism.

⬇️ TSH low: Too much thyroid hormone. You might be overmedicated or overproducing thyroid hormones.

↔️ TSH normal: Your thyroid is functioning well without any added stress.

Free T4 (Functional range: 1.4 - 1.8 ng/dL)

T4, thyroxine, is an inactive or stored form of thyroid hormone, so it's ineffective without being converted to its active form. Free T4 measures the thyroxine in your system that is not bonded to any other molecules or proteins. It hasn't been used up yet, and that's what we want to know - how much thyroid hormone is available to do its job.

  • Total T4 (TT4): Skip this one. Don't confuse Free T3 with Total T4, a T4 count that includes FT4 plus T4 bound to other proteins.

⬆️ FT4 high: Excessive thyroid hormone - overactive thyroid or possibly overmedicated.

⬇️ FT4 low: The thyroid isn't making enough hormone; hypothyroidism/low thyroid function.

↔️ FT4 normal: Your thyroid is creating enough hormone without any added stress.

Free T3 (Functional range: 3.00 - 4.50 pg/mL)

T3, triiodithyronine, is the active form of thyroid hormone, and has been converted by losing an iodine atom from its original T4 form. Free T3 measures similarly to Free T4 in that it tells us how much is still available for use in your body. If it's bound to other proteins, it's already been used up and can't be dedicated to metabolic processes (like creating energy, regulating substances in and out of cells, etc.).

  • Total T3 (TT3): Skip this one. Just like TT4, it tells us how much T3 is circulating altogether, including T3 that's already been used. We're more interested in what's available.

⬆️ FT3 high: Excessive thyroid hormone - overactive thyroid or possibly overmedicated.

⬇️ FT3 low: The thyroid isn't converting enough T4 hormone to the active form; hypothyroidism/low thyroid function. There are many causes.

↔️ FT3 normal: Your thyroid is converting enough hormone without any added stress.

Reverse T3 (Functional range: 9 - 35 ng/dL)

Reverse T3 (RT3) is a look-alike hormone T3, active thyroid hormone, but it does not actually activate any thyroid receptors. It is also generated from T4. Think of it like a key that fits in a lock but can't unlock the door. RT3 also becomes elevated under stress, which slows down the thyroid, metabolism, and you as a whole. You don't need to test RT3 it every time, but if given the opportunity and the price is right, get it. Test RT3 as a baseline if this is your first thyroid test or first in a while.

⬆️ RT3 high: Excessive conversion of T4 to inactive RT3. Might be reflection of your adrenal health and how your body is managing stressors, since RT3 conversion is elevated under stress.

↔️ RT3 normal: Your thyroid is properly converting T4 to T3 and RT3 in optimal ratios. There is always some level of RT3 in your body.

TG Antibodies (Functional range: <1 IU/mL)

Thyroglobulin (TG) is a protein made by the thyroid itself. It's the base building block upon which iodine atoms are attached to create thyroid hormones. Antibodies to thyroglobulin attack and destroy the thyroid's ability to create thyroid hormones. A positive/elevated result is also an indicator for Hashimoto's.

⬆️ TG Ab high: The immune system is attacking/destroying your thyroid, which could indicate a positive Hashimoto's diagnosis. Hashimoto's is the autoimmune form hypothyroidism that affects up to 95% of hypothyroid patients.

TPO Antibodies (Functional range: <9 IU/mL)

Thyroid peroxidase (TPO) is an enzyme in the thyroid that attaches iodine atoms to thyroglobulin to create T4 and T3 hormones. TPO antibodies (also called Anti-TPO) are immune proteins that attack this substance and the thyroid itself. This lab result tells you the severity or strength of the autoimmune attack on your thyroid. A positive/elevated result is also an indicator for Hashimoto's.

⬆️ TPO Ab high: The immune system is attacking/destroying your thyroid, which could indicate a positive Hashimoto's diagnosis. Hashimoto's is the autoimmune form hypothyroidism that affects up to 95% of hypothyroid patients.

If your doctor won't cooperate and collaborate

A Hashimoto's client once told me that she had done her research, we'd discussed a plan, and she was very willing to pay for all the testing -- and then her doctor refused to order the thyroid labs she requested.

Are you willing to accept "because I said so" as an answer?

If your doctor won't be a true partner to you, consider hiring another doctor who keeps an open mind; some of the most talented, well-known doctors with the knowledge and track record of reversing complex conditions are ones that openly admit that they learn from their own patients. After all, who's going to care more about your health than you?

It takes 20 years and dozens, or hundreds, of pieces of literature (and often a culture shift) to bring a concept to mainstream medicine. By the time a doctor adopts a mainstream concept, they're already behind the times while individuals like you me and have experimented with our own health, tried lifestyle strategies, and have seen it work. The concept of leaky gut, or intestinal permeability, is a perfect example of this, but it's been called quackery thousands of times before being embraced only in the past 2-3 years. Since lifestyle factors can help to unwind health imbalances, you can easily get ahead of the curve!

Personally, this is what led me to investigate, research, and take action to regain my thyroid health. I had the support of doctors, but I have to admit that much of it was done solo. I became a sponge - sucking up all the knowledge I could so I could ask questions and propose new angles for my own treatment plan. Most importantly, I became actively involved in my treatment strategy and found a doctor who was a true partner & supporter in the process.

The ability to self-order thyroid lab tests has been an incredible advancement in patient-led care. They may cost more than if you go through insurance, but are a good fit if you can't find or aren't getting the support you need.

So, if you doctor won't help you:

  • Fire your doctor. Work with someone who will truly collaborate and respect your opinion.

  • You can order labs yourself, in most states except Arizona, Indiana, Oklahoma, Alaska, and Hawaii, plus Puerto Rico (of as the writing of this article).

  • Self-order and bring the lab results to your doctor if he/she won't order them directly. When you order online, the lab requisition is electronically sent to Labcorp or Quest, a phlebotomy lab that has locations all over the country. You check in, they draw your blood on the spot, and you get the results in your email within 3-5 days. Each of these panels includes the critical few markers from above, but you may have to add RT3 on some:

  • Ulta Lab Tests (this panel includes RT3 & is most affordable at $125 at the time of publishing. $88 without.)

  • DirectLabs (choose "Free Ts plus TSH and Thyroid Antibodies" - $159. No RT3)

  • MyMedLab (this panel is $159. No RT3)

  • Walk-in Lab (this panel is $190, including RT3 - they always have coupon codes. Choice of Quest or Labcorp)

How Often Should You Test Your Thyroid?

Test roughly every 1-2 months until you are symptom-free. Many strategies require a minimum of 30-45 days of consistency to stabilize and see blood chemistry changes.

Once you hit remission and you're no longer symptomatic (or your antibody count is at normal, low levels), you can test every six months to one year. If you begin noticing symptoms, it's time to test again and note what, in your life, has shifted. Then, call a doctor or a thyroid coach.


About the Author

Stephanie B. is a Functional Medicine Certified Health Coach and Nutritional Therapist at The Summit Coaches. Having tangled with nearly every possible root cause of Hashimoto's, hypothyroidism, and adrenal fatigue personally, she became her own health advocate and achieved Hashimoto's remission, now coaching clients toward the same goal.

"You're not stuck - you're yet to find your way forward."


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