Euthyroid Sick Syndrome, Low T3 & “Normal Thyroid Labs” Explained

Euthyroid sick syndrome is a series of lab abnormalities seen in certain people with an acute or chronic illness. 

Understanding this condition can help explain why so many thyroid patients are unhappy with their current treatment and help us (Doctors and patients) change how we evaluate thyroid treatment. 

In this guide you will learn what ESS is, how it presents, what causes it and if you should be treated if you have this condition

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What is Euthyroid Sick Syndrome?

If you have thyroid disease there's a good chance you may not even be familiar with the term euthyroid sick syndrome. 

But this syndrome is actually incredibly important because the physiology involved in this disorder can shed light on why our current thyroid treatment paradigm is lacking. 

Euthyroid sick syndrome (abbreviated ESS for purposes of this article) is a series of lab abnormalities that is observed in people who are sick or ill or in those who are undergoing surgery or fasting (starvation, etc.) (1).

This condition is also referred to as nonthyroidal illness syndrome or NTIS for short. 

But the name can be somewhat confusing so let's unpack it to better understand the definition. 

Euthyroid is a term used to describe a state of normal thyroid function in the body. 

pathogenesis of euthyroid sick syndrome

'Sick' refers to a condition that the patient is under and 'syndrome' is simply a word to describe a medical state. 

So euthyroid sick syndrome can be re-stated as 'normal thyroid function seen in sick patients'. 

It is very clear, and MOST (if not all) doctors should be aware of this, that illness results in very specific changes to thyroid function that can be seen during routine blood tests. 

Patients with euthyroid sick syndrome present with very specific lab tests which have been classified as the following: 

It is very clear that illness and chronic medical conditions result in these changes to thyroid function which dramatically alter the amount of free circulating thyroid hormone in the body. 

This is the primary reason that Doctors do not order routine thyroid tests on patients that are admitted to the hospital. 

The idea behind this condition is that there is some altered state of thyroid function that occurs due to illness. 

Our current understanding of this condition is that it represents a state of "normal thyroid function" even though your lab tests are abnormal. 

It is believed that changes, due to illness, negatively impact the hypothalamic-pituitary-thyroid axis in such a way that suppresses TRH and TSH production leading to reduced stimulation of the thyroid gland and thus low circulating free thyroid hormones (2).

It's also probable that illness alters thyroid hormone binding levels in the serum, thyroid hormone metabolism and the uptake of thyroid hormone by specific tissues. 

These concepts are incontrovertible, meaning they are not disputed by those who understand scientific literature (3).

After all, we are simply talking about physiology here. 

This begs the question though:

Is it possible to have a euthyroid sick syndrome like changes in those who suffer from CHRONIC medical conditions

And do those changes affect thyroid function negatively to the point that they warrant treatment

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Does ESS Cause Symptoms?

Because ESS is considered a state of "normal thyroid function" you actually wouldn't expect people to have symptoms associated with thyroid disease if they also have ESS. 

This may make sense in the acute setting, but it may fall apart in the chronic setting. 

If you are a patient admitted to the hospital with sepsis or some other critically illness, it may not be easy to identify the cause of your fatigue or lack of energy. 

Your symptoms could easily be attributed to your acute illness. 

But in the chronic setting, we see something different entirely. 

Abnormal serum levels of thyroid lab tests are often found among people with chronic medical conditions or those who have recently undergone weight loss diets (4).

Some of these lab abnormalities may also be associated with abnormal hypothyroid-esque symptoms. 

If you have low T3, low T4 or high reverse T3 then you may experience some of the following symptoms: 

  • Weight gain
  • Cold intolerance
  • Pain
  • Hair loss
  • Cold body temperature
  • Slow heart rate
  • Menstrual problems
  • Fatigue or low energy

Again, it's important to realize that not all people with ESS will experience any symptoms. 

But it's equally important to understand that some people may experience hypothyroid symptoms and it is these people that may require treatment (more on that below)

What causes Chronic Changes to Thyroid Function? 

Why does your body have a mechanism built-in to blunt thyroid function under certain circumstances?

The answer is not clear, but a few theories have emerged. 

One such theory would be that, in an attempt to conserve energy, your body temporarily blunts 

This makes sense in acute illness. 

Why would your body want to put power and energy into growing your hair, maintaining the quality of your skin and so on, if you are currently critically ill and about to die? 

Wouldn't it make more sense to put energy into bolstering your immune system (if you are suffering from an infection), improving cardiac output (if you are suffering from heart issues) or putting energy into healing after surgery (if you are suffering from a wound or trauma)?

Your body is much smarter than you probably realize and it does all of these things without you even thinking about it. 

In response to illness, your body sends signals to the peripheral tissues to reduce the conversion of thyroid hormone into the active T3 thyroid hormone. 

This results in normal to high levels of T4, low levels of T3 and high levels of reverse T3 (5).

This allows your body to titrate how it is expending energy, where energy expenditure should go and probably helps the body to heal. 

All of this information makes a lot of sense if we are talking about a critically ill patient, someone who is in the hospital with a serious problem, but what about patients who are "at home" but still chronically ill?

Is it possible that patients who have multiple illnesses may suffer from a similar set of problems as those people who are critical ill, but perhaps on a different scale or intensity?

T3 conversion booster results

This is exactly what I believe is going on in many patients. 

Consider this example:

What if you are a middle-aged (40-50) female who is 50 pounds overweight?

Maybe you also have prediabetes (6), high cholesterol, slight inflammation in your body and thyroid disease (7).

Is it possible that these metabolic abnormalities are putting strain on the body?

Perhaps enough strain to result in changes in thyroid function and thyroid conversion as your body attempts to fix the many problems you are facing?

While there are MANY reasons that you may have thyroid dysfunction, I believe that one of the most underappreciated conditions that some patients suffer from is low T3 syndrome caused by a chronic ESS like state

This type of syndrome will often be ignored or misdiagnosed by physicians because it doesn't fit the current template of thyroid disease. 

Low T3 vs Euthyroid Sick Syndrome

Low T3 syndrome is a state of thyroid disease which is becoming more and more common. 

You can think of low T3 as a subset of thyroid disorders that falls within the classification of euthyroid sick syndrome. 

The same issues that cause ESS probably cause low T3, but each person may present with slightly different lab studies. 

If we took 10 people and put them under extreme stress we might find that 4 out of the 10 people develop very low T3 levels while 4 out of the 10 people develop both low T3 and low T4

In this way, they are probably variations of the same condition but altered by genetic factors at the individual level. 

In this disease state, the body has difficulty either in producing T3 or converting T3 from the substrate T4 (8).

The problem with this condition is that it's felt to be caused by factors unrelated to thyroid control (such as suppression of the pituitary gland). 

Because of these changes, it is felt that low T3 syndrome is not primarily a thyroid disease. 

And while this is true, it doesn't mean that the person suffering from the condition will get the help they need. 

If your low T3 is caused by inflammation (9), gut dysfunction (10) or nutrient deficiencies, then the only way that it will go away is if you address those problems. 

But when was the last time that your Doctor asked you about any of these? 

Should it be Treated?

Our current understanding of ESS is that patients with this condition should NOT be treated by thyroid hormone. 

Studies have shown that giving patients T4 thyroid medications, even those that are critically ill, show no benefit. 

Other studies have shown, however, that the temporary use of T3 containing medications (such as liothyronine or Cytomel) may have some benefit in certain patients. 

It is clear that low circulating levels of T3 thyroid hormone will have detrimental effects on overall health (11).

In the acute setting, the answer is more clear. 

Treatment will probably not yield better results (12).

But what about in the chronic setting?

What about the person who has low T3 and who is ALSO experiencing hypothyroid symptoms?

This is probably the person that WILL benefit from thyroid hormone replacement (with T3 containing medications). 

Euthyroid sick syndrome is said to be a state of euthyroidism (meaning normal thyroid function) but this name may be a misnomer under certain conditions (13).

It's entirely possible that in some situations that the thyroid lab abnormalities seen in ESS represent normal physiologic changes due to acute illness. 

But it's also possible that chronic suppression of thyroid function, such as seen with chronic medical conditions, may be a pathologic state which would benefit from thyroid hormone treatment. 

So should you be treated if you have low T3 syndrome or euthyroid sick syndrome?

The answer probably depends on the degree of thyroid lab abnormalities that you are experiencing AND if you are also experiencing symptoms associated with your disease. 

In patients who have hypothyroid symptoms (such as weight gain, fatigue, hair loss, constipation and so on) and low T3, low T4 and high reverse T3, thyroid hormone replacement therapy may be beneficial or even necessary. 

Whenever possible, your goal should be to treat underlying dysfunction which may cause the abnormal lab results, but in some cases, this may not be possible

For those who fall into this category, supplementation with T3 medication such as liothyronine or Cytomel may be very helpful. 

The changes we've discussed here may explain why studies do show that very specific people have a robust response to T3 medication while experiencing no benefit when using T4 medication. 

Final Thoughts

It appears that our current understanding of thyroid function and physiology has some room to grow. 

By understanding what happens in euthyroid sick syndrome and in acute illness, we can better understand chronic illness and thyroid hormone dysfunction among patients who are suffering. 

There is a large sub-group of the population with thyroid disease who experience the symptoms of hypothyroidism but still remain untreated due to a normal TSH

This population of people may be suffering from a chronic form of ESS and one which may be dramatically improved with the right treatment. 

I remain convinced that this type of information will become more common over the coming years and patients will have much better outcomes as we expand beyond the current thyroid treatment paradigm

Now I want to hear from you:

Do you have low T3 syndrome or do you suspect you have euthyroid sick syndrome?

Have you been able to get treatment or find relief with any other therapies?

What has worked for you? What hasn't?

Leave your comments below! 

References (Click to Expand)

This post was most recently updated on March 11th, 2019

Dr. Westin Childs

Dr. Westin Childs is a Doctor of Osteopathic Medicine. He provides well-researched actionable information about hormone-related disorders and formulates supplements to treat these disorders.He is trained in Internal Medicine, Functional Medicine, and Integrative Medicine. His focus is on managing thyroid disorders, weight loss resistance, and other sex hormone imbalances.You can read more about his own personal journey here.

12 thoughts on “Euthyroid Sick Syndrome, Low T3 & “Normal Thyroid Labs” Explained”

  1. Dr.Childs
    I had thyroidectomy 16 months ago and have had nothing but constant hideous pains mainly in my Feet,Ankles and knees. I do have off and on pains in one shoulder, upper back and hips but they are random. I do have a life long Autoimmune disease and my Endo keep insisting I’m hyper based on blood test FT4, FT3 (fall in the lab ranges) TSH (low due to thyroid cancer) my Reverse T3 was 19. I feel ok not great but ok and I refuse for them to reduce my synthyroid and cytomel, I’m currently on 100mcg synthyroid and 15mcg Cytomel.

    Can you tell me why endo insist I’m hyper when I have not one single symptom and Im pretty sure I know hyper since I had severe episodes of hyper before thyroidectomy. Sorry so long…grace

  2. Hey Dr. Childs, I’m the bulimic guy who’s asked you a bunch of questions over the last year. At one point, an ND dx’d me with ESS but I was a little hesitant to accept it due to the fact that my reverse T3 was actually low. I had low T3, T4 at the very bottom of the range, normal TSH at that point. Can you have ESS with low RT3? At some point, I started taking Cytomel 50 mcg daily because the hypo symptoms were so bad and I was gaining weight. The T3 helped me stop gaining weight but not return to my baseline. When I went off (to see what would happen), my T3 dropped far below the range, T4 was low, and TSH was high at 5. Interestingly, despite low T3 for years (and symptoms), my TSH had always been normal. I’m back on T3 because I quickly put weight back on and felt terrible. I’m ready to give up caring anyway as nothing I have tried has helped me escape the beast (bulimia). Somewhat relatedly, I did an OAT recently and I seem to have significant clostridia overgrowth among a few other odd results. Any thoughts on the big picture?

  3. Hi Dr Childs,

    I have been off and on phentermine for at least 12 years. I am only 25-30lbs overweight. The first time I lost 30 lbs in 2-3 months. As soon as I stopped taking it the weight came back. Fast forward over the 12 years and I’ve been off and on at least 5 times only to lose 6-8lbs each time and cannot lose more no matter how long I stay on it. I also tried HCG with the same initial 6-8lb loss then no more. I have elevated TSH (but “within normal range”) low T4, low T3 and high reverse T3. I am currently taking no thyroid meds. I have been searching for a good thyroid doctor for eight years. I have seen 16 different physicians to no avail. I cannot find anyone who will treat my thyroid with anything but synthroid. I have given up with conventional medicine at this point and I AM A NURSE!!
    I believe my only choice is to heal myself with supplementation and maybe NDT I can obtain from Europe. What are your suggestions for supplements? I’m certain I have destroyed my metabolism with years of calorie restriction from the phentermine and HCG diets.

    • Hi Suzanne,

      You can look into supplements which help improve thyroid function and treat leptin resistance as a starting point.

  4. I was certain you would say thyroid resistance or insulin resistance. I didn’t expect leptin resistance. I am NEVER hungry. My stomach literally never growls or gives me “hunger pains”.

  5. Hi Dr Childs. I am finding your website so informative! I have really increased my understanding of all things thyroid.

    But quick question . What thyroid issue is involved with low TSH (.11), low t3, low t4 and reverse t3 of 12? I currently have post concussion syndrome, but with these low thyroid values I am almost comatose and have been or on medical leave. But because my TSH is low, my doc won’t address my other lab values and redo my throat needs. I currently take 1.5 grains armour.
    Thank you!

    • Hi Julie,

      Some people are very sensitive to the T3 in NDT which may suppress TSH more than would be considered “normal” without properly increasing free thyroid hormone levels.

  6. Hi, please have no insurance so I want to make the essential tests first. Been diagnosed with hashimotos by the antibodies blood test. Not on any medication but never had reverse 3 tested or adrenals. Dr wants me to do the poop test first. Do you think reverse 3 test first would be best as the mornings are hell, high agitation which lasts many hours what do you think?

  7. Early 20s, (TSH = 1.4 mIU/L) (total t3 = 82 ng/dL) and (Thyroxine-T4 = 3.8 ug/dL).T3 and T4 are a bit low, but with a normal TSH. Is this odd to see without chronic illness and when obesity is not a factor?

    If experiencing fatigue, brain fog, lethargy, and many other symptoms from your checklist… Should one seek thyroid treatment?

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