Thyroid Stimulating Hormone (TSH): Low TSH? Elevated TSH?

TSH or thyroid stimulating hormone is the number one screening tool for disorders of the thyroid gland. The problem is it is a very poor way to assess your thyroid gland function.

In my clinical practice I have found that TSH alone is not enough to assess thyroid function. I have seen people with TSH levels in hypothyroid ranges with little if any hypothyroid symptoms.

More often, I have seen those with many hypothyroid symptoms with completely normal and even optimal TSH levels.

I also see individuals suffering from hyperthyroid symptoms with ranges in TSH levels that are considered optimal.

This of course poses a problem, doesn't it? As someone concerned about your health and fitness, how do you rule out thyroid dysfunction as the cause of your issues if TSH can be so unreliable?

You use your symptoms and further testing as a guide. That is what this blog will teach you how to do.

A brief background on thyroid physiology

Thyroid stimulating hormone is released by the pituitary gland in response to signals from the brain. The hypothalamus receives feedback from thyroid hormones (mostly T4) to either stimulate or suppress TSH release from the pituitary.

Once TSH is released, it interacts in the thyroid gland to increase levels of T4.  T4, called thyroxine, is not active (or is less active), and it serves as a reservoir where active thyroid hormone is formed.

Active thyroid hormone is T3 or triiodothyronine. T3 is the hormone that acts on the metabolism and stimulates cellular activity.

Another part of this story is that T3 and T4 can be found in the body bound to other proteins or free by themselves. Bound T4 cannot be converted to T3 and bound T3 cannot act on tissues. So, the amount of the thyroid binding protein, thyroid binding globulin, has an impact on thyroid function.

Another tricky part of the thyroid story is that T4 can be converted into either T3, which is active thyroid hormone, or reverse T3 (rT3) which is inactive. rT3 levels are elevated in times of increased cortisol, like stress.

Finally, the thyroid receptor has to be available and able to interact with T3. Many things can impact this. But cortisol again gets in on the action here. Adequate cortisol levels may be required for proper function of thyroid receptors.

So, too much cortisol and T3 gets converted to rT3. That's not good. But too little cortisol and T3 has a difficult time acting on its receptors. Also not good.

Hopefully now you can see that there is so much going on with thyroid function and that TSH levels may miss several important issues.

What are normal TSH levels?

There has been debate on this concept for years. Many doctors, including some pretty conservative conventional medical doctors have felt current normal values for TSH are too broad.

The current reference ranges for most labs (reference ranges very slightly based on lab) are .5 to 5.5 for TSH levels.

However, there has been quite a debate over these numbers over the last several years. In 2003 the American Association of Clinical Endocrinologists (AACE) recommended the values be narrowed to .3 to 3.0.

Because hyperthyroid and hypothyroid patients can be diagnosed at higher levels or lower levels of TSH respectively, a 2004 joint consensus recommended against the change.

So how do we make sense of all this? The truth is many savvy clinicians working with thyroid disorders do not overeact to TSH levels. After talking to several of my colleagues, reflecting on my clinical experience and looking at the body of research, here are the conclusions I have come to:

  • Levels between 2 and 4, without symptoms is where the vast majority of patients I work with fall and likely represents a healthy functional level
  • TSH levels between .3 and 3.0, without thyroid symptoms, likely point to healthy thyroid function according to research consensus.
  • Symptoms of hyperthyroid (anxiety, weight loss, increased heart rate, etc) with TSH below 2.0 should be assessed for hyperthyroid. And may want to be assessed regardless of TSH levels.
  • Symptoms of hypothyroid (depression, weight gain, fatigue, mental fog) with TSH levels in the high 2s or low 3s should be assessed for hypothyroid. And an assessment may be smart regardless of TSH.
  • If you had to pin me down on an optimal TSH number, I would probably say 2.
  • The National Academy Of Clinical Biochemistry in 2002 said 2.5.
  • Optimal TSH for someone currently being treated for thyroid is a little different and should be assessed based on symptoms and not solely on numbers.
A prominent leader in the hypothyroid debate, Jeffrey Garber MD, had this to say:

"The TSH normal range should not be a polarizing issue. But as often seen in medicine, it's easier to agree on the extremes. When you get closer to what's marginal, it's a harder call. We need to realize that it's a continuum. If people know that this particular group is more likely to have thyroid disease than the group that's lower, it doesn't commit you to treatment and doesn't say that it's not appropriate, it says to follow it, and maybe intervene."

I tend to agree with that assessment.

Further assessment

So what if your TSH value comes out lower than 5.5, but higher than 2 and you are having thyroid like symptoms? At this point, you may want to get further testing.

Here are the tests I would advise. In order of importance and in my opinion. I have also included some lab values for you. You may have noticed normal lab values for tests online are difficult to come by and sometimes contradictory.

That is because these values are impacted by many things including gender, age and the comparison sample used at that particular lab. So always compare your values to the values on the lab you are using. You can see the resources I used for these numbers at the end of this blog.

  • Free T3. Look for levels between 300- 450 (same as 3.0 -4.5)
  • Free T4. Look for levels between 1.0-1.5
  • Reverse T3. Look for levels of 9.0-35.0
  • T3 Uptake. Look for levels of 28-38
  • Thyroid Antibodies. Look for a negative result
  • Adrenal Stress Index (ASI). Look for a curve that starts high and ends low across the 4 measurements. See below for typical normal values: ASI normals
    Morning cortisol normal = 13-24
    Noon cortisol normal = 5-10
    Afternoon cortisol normal =3-8
    Evening cortisol normal =1-5
    Total cortisol across 4 measurements. normal = 23-42

Let's go through these in detail:

Free T3 and Free T4

As you have learned, bound T3 and T4 can't do their jobs. They have to be released from the carrier proteins first. If you really want to know if you have adequate levels of these hormones, you need free hormone values.

T3 is the hormone that acts on your tissue to produce thyroid effects. T4 acts as a T3 reservoir. Most thyroid hormone in your body is T4 and it must be converted to T3. This happens in the liver, kidneys and digestive tract primarily.

Reverse T3

Remember T3 is the most important since it tells you if there is enough of the biologicaly active thyroid hormone (the one that has the beneficial effects) in the body. T4 is converted to T3, but it can also be converted to rT3 which is inactive.

There are several things that can interfere with T4 conversion to T3 causing increased rT3 instead. These include nutrient deficiencies (such as selenium) and the stress hormone cortisol.

T3 Uptake

This is a confusing test to understand but an important one and one most doctors won't run even if you ask. The reason? It is an old test that many believe to provide no useful information.

But we use it for a different purpose. It can tell you the number of thyroid binding proteins and how T3 levels are being impacted by that. Are there two many carrier proteins binding up all the T3 making it impossible for it to do its job?

Or are there too little, making more T3 available to do its job? In other words, this test gives you an indication why you may being seeing low or high levels of T3.

A T3-uptake that is high means less carrier proteins and more T3 (testosterone and cortisol can cause this). A T3 Uptake that is low, means more carrier proteins and less T3 (estrogen can do this).

Thyroid antibodies

This helps you rule out an autoimmune thyroid issue. This is important because if you are dealing with an immune thyroid interaction, there are steps you can take to deal with it.

I have personally seen those with low thyroid function and positive thyroid antibodies (i.e. a condition called Hashimoto's Thyroid) revert to normal thyroid function and elimination of antibodies through restoring gut function and finding and eliminating food sensitivities and allergies. Most notably, allergies to gluten and the milk protein casein.

Adrenal Stress Index

Given the way cortisol impacts so many aspects of thyroid physiology, it is important to know the amount and rhythm of cortisol exposure in a day. Too high cortisol and you impact T4 to T3 conversion as well as low carrier proteins. Too low cortisol and the thyroid receptors may not be able to interact appropriately with T3.

The adrenal glands have a close relationship with the thyroid gland and each one impacts the function of the other.

Final thoughts

I hope this blog on the TSH test and other aspects of thyroid physiology was helpful. Thyroid and adrenal issues are one of the most common hidden causes of fatigue and stalled weight loss. This is why we built an entire online program that teaches you how to eat exercise, live and supplement in a way that can restore metabolic function by healing the thyroid gland. Check it out below.

  1. Lord, R.S. & Bralley, J.A. (2008) Laboratory Evaluations For Integrative And Functional Medicine. Duluth, Georgia: Metametrix.
  2. Weatherby, R. & Ferguson, S. (2002) Blood Chemistry & CBC Analysis- Clinical Laboratory Testing From A Functional Perspective. Jacksonville, Oregon: Vis Medicatrix Press
  3. Kharrazian, D. (2010) Why Do I Still Have Thyroid Symptoms? When My Lab test Are Normal. Garden City, New York: Morgan James Publishing.

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