Help for Autoimmunity, Brain, Metabolic, and Hormone Health, Digestion, and Beyond

Thyroid testing – you must test T3

Short version: If your doctor is checking your TSH and …

Short version: If your doctor is checking your TSH and T4, and isn’t checking your T3, they have no idea how your thyroid is functioning.

Maybe you’re tired.. all the time. Maybe, hair is getting thinner or weight has crept up? Or, maybe there’s hair growing in places you don’t want it to grow? These are some of the more common symptoms that get brought up that will lead doctors to check for low thyroid function. On the flip side of that, maybe you’re anxious all the time – can’t sleep, are rapidly losing weight, and your eyes just don’t look like they used to. These are some of the reasons why your doctor might check for overactive thyroid – which is, far less common.

So, you’ve had the fateful visit with your PCP and blood gets drawn. You come back for the results and they proclaim you “normal”. All lab values are “within range”. Your thyroid function is “just fine”.

Let’s break that down.

It’s standard protocol in mainstream medicine to check TSH (thyroid stimulating hormone) and T4 (thyroxine) to assess thyroid function. To explore this a little bit more – let’s look at what these two hormones are.

TSH (thyroid stimulating hormone)

TSH is produced by the anterior pituitary gland – which sits in a little niche in about the middle of your skull. This part of the pituitary gland produces a number of hormones. TSH is one of them, and is produced in response to a hormone called Thyrotropin Releasing Hormone (TRH) that’s produced by the Hypothalamus. The Hypothalamus and the Pituitary work together to control or influence MANY bodily functions. TSH’s main function is to stimulate the thyroid gland to produce thyroid hormones.

T4 (thyroxine or tetraiodothyronine)

T4 is the main hormone produced by the thyroid gland. Depending on whose research you read, anywhere from 80% (at the low end) to 93% (at the higher end) of the hormones produced by the thyroid gland consists of T4. Ok, so far it sounds like this would be smart to test.. but………. T4 is NOT THE active thyroid hormone. T4 functions as a prohormone – or precursor hormone for T3 – which is THE active thyroid hormone.

T3 (tri-iodothyronine)

As previously mentioned, T3 is THE active thyroid hormone. T3 preferentially binds to thyroid receptors (some of which are mistakenly called Thyroxine receptors – even though they don’t bind Thyroxine aka T4) that exist on the mitochondrial membrane (remember that the mitochondria is the powerhouse of the cell!), and on the outside of the cell’s nucleus. Thyroid receptors are found on all metabolically active cells and in nearly all cells (found one mention of them potentially not being found in the testes – but no research to back that up). A notable exception would be red blood cells, which are lacking many of the cellular structures that other cells have – since their primary purpose is oxygen transport. When T3 meets a Thyroid receptor, the end results are increased metabolism (of energy, including carbohydrates, fats, and proteins), organ development, growth, and function of neurotransmitters called catecholamines (dopamine, epinephrine, norepinephrine).

Basically, when T3 hits a cell, energy gets used (leaving out the mechanics of receptors, cell signaling, etc). If it doesn’t get used, it gets stored. If energy doesn’t get used and gets stored instead, ya got no energy!

T4 to T3?

Ok, so – if the thyroid produces loads of T4 and not a lot of T3, yet all of my cells take T3 to do – well, anything – then how does the T4 get converted to T3? Well, that happens primarily in – the liver. Some also takes place in the kidneys, the brain, and in muscle tissue. Why is this important? Well, if there’s anything going on with the liver, then your T4 to T3 conversion is just going to be bad. Examples: alcohol consumption, blood sugar issues, latent immune dysfunction, gallbladder issues, general inflammation, medication use – you get the picture.

Ok, so, why is my doctor checking T4 (the inactive thyroid hormone) and TSH (a hormone produced by a completely separate gland in the base of my skull) to try to assess my thyroid function? My best answer? Beats the &*$% out of me! While yes, assessing T4 would make sense to see if the thyroid is doing anything, not testing T3 makes absolutely no sense – because THAT is the function we’re trying to figure out. THAT is THE active thyroid hormone. THAT is what is determining whether my body uses the energy that it takes in, and whether I feel like I have any energy at all.

Is there any merit in checking TSH?

Well, the short answer is that there can be. TSH CAN be high (or low) through feedback loops. The “idea” is that if TSH is high, that the pituitary gland is screaming at the thyroid to get up off its proverbial butt and actually do something – make some, or make some more thyroid hormone. If TSH is high, it’s assumed that you have hypothyroidism – with or without checking T3. The problem is that it’s not that simple – because, as you’ve just learned, T4 is converted to T3 ELSEWHERE from the thyroid gland. Does it provide some information? Sure. But nowhere near all of it. And also NOT an accurate or complete assessment of poor thyroid function, conversion, or availability of thyroid hormone.

Is there any merit in checking T4?

That’s even more debatable. The idea behind checking T4 is that you’re assuming that T4 will be converted to T3 in appropriate amounts, AND that it’s available to all of the cells that need/use it. Notsomuch. A whole lot of factors have to be functioning properly for this to happen. Sometimes the answer is – save your money for testing what’s actually important. Is it sometimes that not enough T4 is produced to convert to T3? Yes. Sometimes that’s the case. But – not usually.

And when we don’t convert to T3? Well, that’s another post…

So, what do I do if my practitioner won’t test my T3?

Well, I’d strongly recommend finding another practitioner. If you can’t, and you’re working inside an insurance model (i.e. using health insurance to cover your testing), AND your practitioner isn’t willing to add T3 to your lab orders, there are loads of different directions you can go. Besides finding a complimentary practitioner (shout out to functional medicine) that WILL do the testing for you (maybe or maybe not covered by insurance), you can order lab tests without a doctor’s order. It’s not as expensive as you might imagine. Many will order them at cost (my policy) and many work with labs that discount testing (often to prices less than what insurance charges or with deductible/copay costs) and/or have relationships with licensed practitioners in other states – allowing ordering across state lines.

Lab Groups through practitioners
(look for practitioners that use these companies)

Evexia Diagnostics – https://www.evexiadiagnostics.com/
FullScript/Rupa Health – https://www.rupahealth.com/

Self-order lab companies
(or search for direct to consumer labs or self-order lab companies)

LabCorp On Demand – https://www.ondemand.labcorp.com/
QuestHealth –https://www.questhealth.com/
AnyLabTestNow –https://www.anylabtestnow.com

There will be a lot more on thyroid function, testing, hypothyroidism and hyperthyroidism, and autoimmunity to come.
We’re just getting started.

A little light reference reading:

https://www.ncbi.nlm.nih.gov/books/NBK499850/
https://pmc.ncbi.nlm.nih.gov/articles/PMC6599431/
https://www.sciencedirect.com/science/article/abs/pii/S004763742030141X
https://pmc.ncbi.nlm.nih.gov/articles/PMC5843491/
https://www.ncbi.nlm.nih.gov/books/NBK537039/
https://www.ncbi.nlm.nih.gov/books/NBK285545/
https://www.ncbi.nlm.nih.gov/books/NBK500006/
https://thyroidresearchjournal.biomedcentral.com/articles/10.1186/1756-6614-4-S1-S9
https://www.ncbi.nlm.nih.gov/books/NBK535380/

drandrealotken

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