What is Reverse T3? (And Why Your Doctor Won't Order It)

What is Reverse T3? (And Why Your Doctor Won’t Order It)

What is Reverse T3?

We are going back to the basics today to talk about one of the MOST important thyroid lab tests that many of you probably have never heard about. 

I know what you're thinking...

If it's so important, why hasn't my doctor ordered it and why haven't I heard about it?

I'm going to explain the reason for that in a minute, but for now, let's talk about some of the basics of reverse T3

It's best to understand reverse T3 in the context of thyroid physiology

And thyroid physiology is just a fancy way of referring to how the thyroid gland functions in your body from start to finish. 

You see, most doctors only ever focus on something called the TSH which is produced from your brain. 

But if your doctor only focuses on the TSH, he or she will miss out on tons of other relevant and important information that can be found downstream. 

To put this into context, let's define some basic thyroid terms: 

  • TSH - TSH stands for thyroid stimulating hormone and it is produced in the pituitary gland in your brain. It acts to stimulate the thyroid gland to tell it to produce more thyroid hormone. 
  • Free T4 - Free T4 is one of two active thyroid hormones produced by the thyroid gland. What you need to know is that T4 is NOT active by itself and must be converted into T3. 
  • Free T3 - T3 is the most powerful and potent thyroid hormone in your body. Most of it is created when your body turns T4 into T3. 
  • Reverse T3 - Reverse T3 is an anti-thyroid metabolite that acts to completely BLOCK your thyroid from working. Reverse T3 is created by the body from T4. Your body can either turn T4 into T3 or into reverse T3 based on what it needs. 

It's VERY important for you to understand these 4 different aspects of thyroid function so if this is your first time reading about them make sure you read them again to let it sink in. 

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What information Does Reverse T3 Give You?

Once you do that you may be asking yourself this question:

"Why does my body even produce reverse T3?"

The answer is simple!

Reverse T3 is created by the body as a way to manage and control how much thyroid hormone your body can use at any given time. 

If your body didn't have reverse T3 then it would be very easy for your body to accidentally pump out too much thyroid hormone which would send you into hyperthyroidism

Reverse T3 helps your body carefully determine how much thyroid hormone is active at any given time. 

But this is where the problems begin...

Certain conditions can hijack this system and cause it to run haywire. 

These conditions then create a situation in which your thyroid is artificially slowed down. 

The slower your thyroid is the harder it will be for you to feel better. 

So when you check for reverse T3 it gives you some valuable information about how well your body is using thyroid hormone. 

If, for instance, you order your reverse T3 level and find that it is quite high (which is a bad thing, by the way) you will know that your body is having trouble converting T4 into the active thyroid hormone T3. 

If, on the other hand, you order your reverse T3 level and find that it is quite low (which is sometimes a good thing) you will know that your body is NOT having trouble producing the active thyroid hormone T3. 

The process by which your body takes T4 and turns it into either T3 or reverse T3 is known as thyroid conversion

And checking your reverse T3 gives you valuable information about how well this process is occurring in your body. 

Why Won't My Doctor Order Reverse T3?

If this information is so helpful, why hasn't my doctor ordered this test for me?

That is the question of the decade and one that I will demystify for you right now! 

The answer is actually very simple:

Doctors, especially endocrinologists, have already made up their minds about testing and managing thyroid problems. 

They believe that the only test necessary to evaluate the thyroid is the TSH and that all other additional tests provide no further useful information. 

This mode of thyroid management is referred to as the "standard of care" (1). 

And the standard of care is the methodology behind treating any given disease state. 

It just so happens that the standard of care for thyroid management (treating low thyroid) is to test for the TSH (2) and provide treatment in the form of levothyroxine (3). 

The problem with this standard is that it does NOT work for everyone. 

There are plenty of thyroid patients who do not respond well to this standard who continue to experience thyroid symptoms despite having a normal TSH. 

It is THESE patients that we are primarily concerned about here. 

Reverse T3 can be used to help provide additional information for patients who are otherwise not responding to this standard. 

How do you know if you fall into this category? 

It's simple. 

If you are someone who is faithfully taking your thyroid medication and still experiencing symptoms such as weight gain, fatigue, hair loss, constipation, etc. then you would benefit from the use of reverse T3. 

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Even though you may benefit from the additional information that reverse T3 testing provides, it may still be difficult to get your doctor to order it. 

Because doctors are not accustomed to ordering the reverse T3, they have a hard time interpreting or understanding the results that it provides. 

So even if you do manage to get your doctor to order it, it's unlikely that they will have anything insightful about the results once you do. 

The good news is that you don't need them. 

I have provided plenty of free resources on my blog and in the form of videos and articles that walk you through exactly how to interpret your reverse T3 lab results

Why Every Thyroid Patient Needs To Get Reverse T3 Tested

I consider reverse T3 to be one of the most important thyroid lab tests available because of the information it gives you about thyroid conversion. 

Remember:

Thyroid conversion is a process going on in your body at ALL times and it's the process your body uses to activate thyroid hormone. 

This process is separate and different from the process of TSH production which is what most doctors focus on. 

To get a clear picture of thyroid function in your body you need to get all of the available thyroid lab tests. 

It's both possible, and likely, for instance, that even though your TSH level is normal, your body may still have problems converting T4 into T3. 

If reverse T3 levels build up in your body, then it doesn't matter how much free T3 is available. 

Reverse T3 will act to block that free T3 and it will prevent your body from feeling better. 

Thyroid Medication & Your Reverse T3 Level

Knowing that your reverse T3 is high, for instance, can also give you information about what type of thyroid medication would be best for you. 

Thyroid patients who have a normal or low reverse T3 level tend to do just fine taking T4 only thyroid medications like levothyroxine and Synthroid. 

Thyroid patients who have a high reverse T3, on the other hand, tend to do better on medications that contain T3 thyroid hormone. 

Certain thyroid medications, such as Cytomel and liothyronine, contain the active T3 thyroid hormone directly. 

And by using these powerful medications you can completely bypass the thyroid conversion process. 

Taking pure T3 thyroid medications will drive down reverse T3 levels as they do. 

Switching up your thyroid medication isn't the only way to manage reverse T3 issues, however!

Other natural treatments such as changing up your diet, reducing inflammation in your body, regular exercise, and even taking certain supplements can all help to improve your reverse T3. 

Final Thoughts

Reverse T3 testing is something that you can look at every single time you get your thyroid lab tests drawn. 

The next time you are scheduled to get your TSH checked, make sure to ask for your free T4, free T3, and reverse T3 as well. 

Now I want to hear from you:

Is this the first time you've heard about reverse T3 testing? 

Do you feel like you understand how important reverse T3 testing is for your thyroid?

Are you planning on asking your doctor to order this test for you the next time you go in?

Leave your questions or comments below! 

References (Click to Expand)

the thyroid lab test that ever thyroid patient needs

Dr. Westin Childs

About Dr. Westin Childs

Hey! I'm Westin Childs D.O. (former Osteopathic Physician). I don't practice medicine anymore and instead specialize in helping people like YOU who have thyroid problems, hormone imbalances, and weight loss resistance. I love to write and share what I've learned over the years. I also happen to formulate the best supplements on the market (well, at least in my opinion!) and I'm proud to say that over 45,000+ people have used them over the last 4.5 years. You can read more about my own personal health journey and why I am so passionate about what I do here.

38 thoughts on “What is Reverse T3? (And Why Your Doctor Won’t Order It)”

  1. Hi Dr. Childs,
    I’m not currently on any medication and am believed third stage adrenal fatigue.
    TSH 3.55
    T4 1.43
    T3 3.5
    Reverse T3 16.1
    TPO <9
    Cortisol am low 5.5

    Weight gain and inibility to lose weight. Thoughts? Thank you!

    Reply
    • Hi Lee,

      You are 100% correct which is why that second link is included 🙂 I’m illustrating the point that conventional doctors only believe in the TSH and this is what leads them to believe they don’t need to test for the reverse T3. The contradiction is the fact that so many thyroid patients continue to suffer from thyroid symptoms despite having a normal TSH which invalidates that point of view. If it were true that the TSH is the only thing needed then thyroid patients wouldn’t have a need to seek out further info or add additional tests.

      The first link is included just to teach the reader about the standard of care so they understand what it actually means and how it drives pretty much all treatment in any given specialty. It’s not something specific to the thyroid but more general about all specialties within medicine. But the standard of care is what prevents doctors from being able to look beyond the TSH which is why it’s important to this conversation.

      Reply
  2. Having a thyroid problem isn’t new to me. What is new to me is that there are other tests that can be taken. I’ve asked my dr. before and she says exactly what you said above. “the standard of care” is a funny name for it because it isn’t care at all. I have had hypothyroidism since I was 20. I am now going to be 65. I have never felt good. I always have a hard time losing weight and for 5 years now, I just keep increasing in weight. I am always tired, irritable, can’t sleep but can fall asleep at any time during the day. My skin is always dry and my hair has fallen out. I have to do something. My annual physical is coming up and I am sending a message to the dr before then. Either she orders these tests or I will find another dr who will. I am fed up.
    I am on Levothyroxine and have been since being diagnosed. Nothing is helping and now I know why. I have downloaded some of your free information and I will be bringing it with me to my appointment. Thank you for opening my eyes! I will research more and will be coming to you for supplements after I find out what the dr says.

    Reply
  3. My son will be 9 yrs old with Down Syndrome and diagnosed at 6 months old with Hypothyroidism. His medication is Levothyroxine 25mcg Mon-Friday and 37.5mcg Sat & Sunday . His TSH is going up and his T4 is staying in a good range. I just got off the phone with his doctor and she said, they don’t run a T3 or Reverse T3 on kids, Why? He has gained weight around 5-8 pounds since the pandemic, maybe a little more, but the doctors don’t seem concerned. He is not fatigue and his BM’s are normal. Do I need to worry about his TSH?
    TSH( max is 5.000 uIU/mL)
    3.905 10/19/18
    4.252 6/11/19
    4.258 12/30/19
    5.529 2/2/21
    T4 Free (max 1.4 ng/dL) same dates as above
    1.0
    0.9
    1.1
    1.1

    Reply
  4. I was exposed to mold at a previous employer and have developed numerous Autoimmune problems including, Hypothyroidism, Asthma, Arthritis, and psoriasis, which effects my forehead, nose, and outer ear skin. I was originally prescribed Levothyroxine and it did not help. I researched my condition and found that many people do not benefit from this and should try other medications such as NP Thyroid. I requested this and was prescribed it. I noticed a small improvement but still had extreme exhaustion and weight gain. I was referred to an Endocrinologist and requested Liothyronine. He originally started me out on 5 mcg 5 times a day. I noticed more improvement. My blood work came back with low T4 levels, TSH within range, and T3 at the lower end of the accepted scale. I requested and received an increase to 25 mcg daily and symptoms still about the same. This is when I found out about RT3. I asked the Doctor, based upon everything I have read, with each physician stating that RT3 should be done as part of any Thyroid bloodwork, including cholesterol levels, due to the fact that my levels have been high since the Thyroid problem. I was told that I probably read my information on the internet and RT3 and cholesterol levels are not important tests for Thyroid problems and the sites I was finding my information didn’t know what they were talking about. My PCP has requested cholesterol tests and it has shown my levels dropping into normal range since starting the Liothyronine. My question is, is it possible for the small amount of T4 being produced is being converted to RT3, preventing me from receiving the full benefits of the Liothyronine? If so, should I request the Iodine pill to cause my Thyroid to become completely non functioning so as to prevent RT3 from interfering with my meds? I am currently taking 50 mcg of Liothyronine.

    Reply
    • Hi Greg,

      It’s always possible but not very likely. I would caution against RAI for the reasons you’ve suggested here. It’s significantly more difficult to optimize thyroid function post-RAI/thyroidectomy.

      Reply
  5. Hi, my name is pat so I got tested for RT3 and it’s 6.4 and low. My FT3 is 3,5 and within and FT4 is 0.64 within lab but low. I’m on 120 t4 and 30mg of t3 however still sooooooo tired , hair loss light panic attack. I fell so depressed cause I don’t know what else to take or do.

    Reply
    • Hi Pat,

      I would start with some natural therapies. Therapies like changing up your diet and taking thyroid enhancing supplements can go a long way to helping you feel better 🙂

      Reply
  6. Hello! I am so grateful for your information! I am on my 3rd doctor! They look at my TSH only. Finally ran my own labs thru LIfe Extension.

    Reverse T3 – 5.8
    TSH -1.130
    T4 Free -.76
    Free T3 – 1.9

    Would I look to only supplement T4 or T4 and T3? I think I read where you said that if Reverse T3 is low, the body is able to convert T4 to T3. Do I have this correct?

    Thanks so much!

    Reply
  7. Thank you, Dr. Child’s! After reading this (and suffering from bloating, constipation, hair loss and recent weight creep) I asked my Endocronologist to run more tests and they refused. I found a wonderful functional health Dr who ran a full slate of tests and found I have very high Rt3. She put me on cytomel, a bunch of supplements to support my thyroid and adrenals and a paleo diet to help reduce inflammation. I was shocked at the visceral reaction of my endocrinologist when I asked for more tests, but was prepared thanks to your warnings. I appreciate you!

    Reply
  8. Hello Dr. Childs,

    I hope you are well. Do you think drinking coffee daily or using testosterone cream can increase reverse T3? What supplements do you recommend for decreasing RT3? Thank you!

    Catherine

    Reply
  9. I am on 60 mg of NatureThyroid x 1 year.
    TSH. 1.39
    Free T4. 1.33
    ReverseT3. 19.8. (Ordered at my request)
    He did not order a free T3. What is my next move?

    Reply
  10. I am having hight RT3 and FT3 lately and my TSH has been low. I also found out that I have one of the MTHFR gene mutations. My Vit B12 on the labs shows to be very high. I have been experiencing awful air hunger out of nowhere. I have never had this. I have also never had high T3 labs either until now. My doctor dropped my Cytomel dose but it has not helped the air hunger. After reading your articles, I think you are saying that I need more T3 rather than dropping the dose. I am so confused as to what is going on and nothing seems to be helping. Can you comment on this please. Thanks.

    Reply
    • Hi Michelle,

      Both dropping your T3 dose and increasing your T3 dose have the potential to lower your rT3 lab test. Which one you need to do depends on a lot of other factors including whether or not you are being overdosed.

      Reply
  11. Hi Dr Childs

    I’ve been dealing with hypothyroidism for about 10 years. I finally found a doctor to request a Reverse T3 along with the stand 3 tests. I started out on Synthroid and was switched about 7 years ago to Amour Thyroid. I have been experiencing the typical fatigue, weight gain, hair loss lack of sleep etc. with no luck at getting my dosage changed from 30mcg of AT. This new doctor changed my dosage from 30 to 45 and I am beginning to feel less fatigue and sleeping better. Here are my latest lab results and I’m wondering if this dosage will be enough or should I be looking at a different medication all together. This is the first time I had a Reverse T3 done in all of the 10 years.

    TSH: 3.180
    T3: 3.1
    T4: 1.14
    RT3: 27.7 (I was quite surprised at this result)

    Any input is great appreciated

    Thank you
    Lynn

    Reply
    • Hi Lynn,

      Thyroid lab tests without a complete medical history aren’t very helpful. You have to look at your lab tests in concert with your history and symptoms to best figure out what medications/doses/etc. work best for your body.

      Reply
  12. I was fortunate that I found a dr. willing to do all of the testing for thyroid. I was put on cytomel after using only levothyroxine. I knew my numbers showed I was slightly over medicated, but when I asked about my eyes feeling buggy and if I should lower the levothyroxine, neither opthmologist or family doctor were concerned, but my eyes were sore and couldn’t focus. They told me I wasn’t understanding how RT3 worked, but I decided to do a 30 day trial lower my levothyroxine to only 3/4 of my dose and see if it helped my eyes. all of my numbers came into the normal range including RT3 for the first time in almost 10 years. Since changing my dosage, I’ve now lost 25 pounds in the last 8 months, my eyes don’t hurt, and I am not nearly as volatile. If it wouldn’t be for a doctor willing to allow me to check my theory, I’d be so sick. By me advocating for my needs against the wishes of my dr. I would never have found how to make this better, even if I still have to take meds. my family doctor has now adjusted my prescriptions so I no longer have to split pills, but patients should not have to work this hard to get the right medicine.

    Reply
    • Hi Debbie,

      Glad you found out what worked for you! As an aside, it will always be the case that other people will never care as much about your health as you do so it’s always worthwhile to spend time and energy making sure you are on the right track. You can never count on your doctor to spend hours after work researching your medical condition but that is definitely something that you can do and it has the potential to be a huge help.

      Reply
  13. I go to a Functional doctor and she’s ignored my high RT3 (that I order) for three years. Now it’s at 29 and I just give up.

    Reply
  14. Excellent information doctor. I want a clarification whether thyroid hormones vary all the day or remain constant for several days and months

    Reply
  15. Will your T4 to T3 conversion supplement still work since my thyroid has shrunk and basically shut down from 30+ years of taking thyroid medication?

    Reply
    • Hi Joyce,

      Yes, T3 conversion occurs outside of the thyroid gland so the supplement works for everyone, including those without a functioning thyroid gland 🙂

      Reply
  16. Hi Dr Child’s your article about the importance of reverse T3 being tested has certainly thrown a spanner in to the works of thyroid physiology!!!
    I am registered here in the UK with a thyroid support group who regard reverse T3 testing as pointless. Clearly reverse T3 testing is not pointless as it is part of a complete thyroid testing picture which helps to determine, as pointed out in your article, if thyroid medication etc is working well.
    You article relates to people with their thyroid intact who are medicated.
    How does the article apply to people who have had a thyroidectomy?

    Reply
    • Hi Jean,

      The same information applies to those without a thyroid as they must be taking thyroid medication and, usually, that medication comes in the form of T4.

      Reply
    • Hi Jean

      I also had a thyroidectomy (supposedly sub-total) decades ago in Australia. Never been able to find doctors who know enough, until recently. I’d been feeling very unwell (hypo) for some time, despite blood tests showing high levels of T4. Had to change doctors twice to finally get an RT3 test. The result was almost double what it should have been and the highest result my doctor had seen in his entire career. I’d been prescribed T4 my whole life and it wasn’t working. Was put on T3 (Tertroxin-liothyronine sodium) with a lower dose of T4 and it made an enormous difference – was like living in two different universes! I felt normal again. RT3 is certainly not a waste of time but as Dr Childs says, extremely important. Very disappointing to hear you have a support group that thinks it is pointless. Perhaps you can find one that understands its importance.

      Reply
  17. I don’t see any mention of low Reverse T3.
    My Reverse T3 is only 7
    free T3 is 3.4
    free T4 is 0.8
    TSH is 5.83
    wondering what is wrong I am on Armour thyroid 90mg

    Reply
    • Hi Rachel,

      Reverse T3 can go low if you have insufficient thyroid hormone floating around in your body which it sounds like you may given your elevated TSH.

      Reply
    • Hi Nancy,

      It depends on whether you are referring to T3 supplements or T3 thyroid medication. Can you please clarify what you mean by T3 supplement?

      T3 supplements (over the counters) are usually best in the morning and T3 medication is usually best taken at night or in the morning.

      Reply

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