4 Conditions that make TSH Levels Inaccurate + "Optimal" Ranges & More

4 Conditions that make TSH Levels Inaccurate + “Optimal” Ranges & More

This guide will walk you through everything you need to know about the TSH including why it isn't always the best marker of thyroid function in the body and which conditions make the interpretation of TSH less accurate. You will also learn more reliable ways to test thyroid status in your body.

TSH might be one of the worst ways to evaluate thyroid function and yet it is probably the most widely used thyroid lab test out there. 


In an attempt to oversimplify thyroid function and management Doctors have become reliant upon TSH testing, but what if there was a better way?

A way that rectifies the fact that so many patients have a "normal" TSH but clearly have hypothyroid symptoms... 

Sound too good to be true? 

It isn't. 

And we are going to talk about it in detail below. 

In this post we will discuss why TSH levels are NOT the best way to evaluate your thyroid function, but more importantly we are going to talk about how to actually assess thyroid function and which lab tests you need...


​Is your TSH Normal?

​This is probably one of the most common questions I get on a daily basis (or some variation of are my lab tests normal). 

Just take a look at the comment section of any post and you will find plenty of people posting their labs with that exact question.

​So let's answer it once and for all. 

Is your TSH actually normal?

​In order to find out if it is normal we have to first understand what this test is actually testing for. 

Don't worry, we aren't going to jump into advanced thyroid physiology (you can find more about that here if you'd like) instead I want to keep things basic:

TSH stands for Thyroid Stimulating Hormone and it comes from the pituitary.

The pituitary is a ​gland in your brain that attempts to tell your thyroid how much thyroid hormone to produce

So why do Doctors care what the pituitary is telling your thyroid gland?

Well TSH turns out to be a quick and dirty way to diagnose both hypothyroidism and hyperthyroidism but it falls short when things get a little more complex.

In the case a standard hypothyroidism your TSH increases.

In the case of standard hyperthyroidism your TSH decreases.

T3 conversion booster results

​But what about the non standard cases. 

What about patients who have normal TSH levels but every hypothyroid symptom?

Does the TSH work for everyone?

Not really and here's why:

When we talk about any hormone we really need to understand how and where the hormone has action in the body.

Thyroid hormone is activated inside the cell of the target tissues and it does this through a nuclear receptor (actually thyroid hormone has both genomic and non genomic actions but the genomic actions are particularly important for symptomatic control). 

In simple words it means that thyroid hormone gets inside the cell and directly turns on genetic transcription (it changes your DNA/RNA directly).

Nuclear action of thyroid hormones at the cellular level, both genomic and non genomic actions

​And this is good, but what is important here is that each tissue has a DIFFERENT demand for thyroid hormone depending on the situation. 

Again, let's put this into simple terms...

If you are incredibly sick in the ICU of a hospital, does it make sense for your body to put energy into growing your hair follicles or making your nails strong?

Not really...

Instead, each of your cells in your body has a different demand for thyroid hormone depending on the situation, time of day, stress you are under, etc.

So how does this fit in with the pituitary gland?

Well the pituitary gland is just another tissue in the body which has a demand for thyroid hormone and a sensitivity to thyroid hormone.

The downside is that unlike other tissues in the body the pituitary is the MOST sensitive tissue to thyroid hormone in your body.

It has a different set of deiodinases (these are the enzymes which either activate or inactivate thyroid hormone). 

Without making it too complex the pituitary gland has only the enzyme which ACTIVATES thyroid hormone. 

Nutrients required for thyroid function

Now compare that to other tissues in the body which have the ability to both INACTIVATE and ACTIVATE thyroid hormone (your body does this through increasing or decreasing reverse T3 levels). 

It's like the pituitary gland has one switch and it's the "on" switch. 

That means if thyroid hormone is floating around in your body it will eventually make it to the thyroid gland which will cause your TSH to drop. 

But that does NOT mean that the other tissues in your body are getting enough thyroid hormone. 

Instead it's usually the opposite...​

Normal vs Optimal TSH Range

Now having said all of those things it doesn't mean that the TSH is entirely useless (in fact I will talk about how it can actually help somewhat helpful later). 

But in order to understand how to evaluate your TSH you need to understand that there is a huge difference between being "normal" and being "optimal".

To start with I have never seen a healthy individual with a TSH > 1.0.

This would indicate, at least subjectively, that the ideal TSH (provided disease is not present in any form) is somewhere around 1.0. 

​Nowadays due to the Standard American Diet, decreased activity levels, absurd rates of insulin resistance and many other factors it is truly rare to see a "healthy" person. 

Standard american diet

That means we need to change our definition of "normal". 

If you look at laboratory tests you will see that a normal TSH level generally falls within 0.5 to 4.5 (or some small variation).

You can see the range from different lab tests below: 

Abnormal TSH kathy

​As you can see the TSH reference range is 0.35 to 5.5

You can see we have a problem here. 

Truly "healthy" people have a TSH < 1.0 and yet the "normal" range extends all the way out beyond 5 in this case. 

That means your Doctor won't flag your TSH as abnormal unless it falls outside of those reference ranges. 

​But as I mentioned above it is important to consider that your pituitary is the MOST sensitive tissue to thyroid hormone in your body. 

That means it is entirely possible to have a "normal" but less than "optimal" TSH.

By these new standards, you can consider a TSH which is greater than 2.0 to be an early indicator of some thyroid dysfunction in the body.

It certainly doesn't mean that anything < 1.0 is "normal" (we need your other thyroid and hormone lab tests to determine that), but it does give us some guidance in terms of understanding how someone can be inside the standard reference range and still have symptoms. 

​This is where things can get a little more complicated. 

There are several conditions where the TSH can be decidedly "normal" in fact it can even be sometimes < 1.0 but the patient can still be hypothyroid.

These conditions include:

​Unfortunately patients who fall into any of these categories tend to get misdiagnosed and/or mismanaged by providers who rely solely on TSH levels for diagnosis. 

  • Bottom line: The "Optimal" range for TSH should be < 2.0, anything higher indicates potential hypothyroidism. Do NOT use the standard lab reference range as your definition of "optimal"

Let's go through some examples so you have a better idea of what I am talking about...

Low T3 Syndrome

​Low T3 syndrome is exactly as it sounds. 

Patients have low T3 but the problem is that they have a relatively preserved TSH (in the normal or even optimal range), but free T3 levels that are either in the low end of the reference range or barely below it

You can see the example below which shows a free T3 level of 2.5 with the reference range from 2.3 to 4.2.

Hypothyroid lab tests

This is a big problem because T3 is the ACTIVE thyroid hormone.

So low levels of this hormone in your blood ​mean you will have low levels of active thyroid hormone despite whatever your TSH may be. 

​Low T3 syndrome is known by many names, and you can read more about it here.

Basically what happen is your body decreases the amount of free T3 and increases the amount of reverse T3 in your body. 

This is felt to be a protective mechanism to conserve energy when your body is under extreme stress.

The problem is that this condition extends beyond the typical acute illness that so many Doctors relate it to.

In fact it has been shown that calorie restriction can even cause low T3 syndrome.

Answer this question:

Have you gone through a calorie restricted diet in your life? Have you gone through the HCG diet or some other medically assisted weight loss program?

And in case you are wondering here are other conditions that can cause Low T3 syndrome and put the "brakes" on your thyroid function:

  • Chronic yo-yo dieting or caloric deprivation leading to starvation
  • Chronic illness, infection or autoimmune disease
  • Chronic medical conditions like Diabetes, cardiovascular disease, metabolic syndrome, etc.

If so, then there is a good chance you may have low T3 syndrome which is causing hypothyroidism but NOT altering your TSH. ​

​Fortunately it is relatively easy to check for and just requires the complete thyroid panel which we will be going over below. 

High TSH but Normal T4

​Another subset of patients have what would be considered subclinical hypothyroidism where their TSH is absolutely elevated (even the conventionally trained physician would agree) but their free T4 is relatively preserved. 

Let me show you an example below: ​

Abnormal TSH kathy

This TSH is elevated at > 3.0 which most physicians would agree is suboptimal (in fact some providers have recommended we change the range to include anything > 2.5 as abnormal)

normal T4 but high TSH

​And yet despite the fact that the TSH is > 3.0 in this case their free T4 is still relatively normal at 1.17 with a reference range of 0.89 to 1.76. 

Occasionally this scenario will prompt a physician to simply recheck the thyroid lab tests within a month without proper treatment with thyroid hormone. 

And patients who are in this situation feel frustrated because they are symptomatic with abnormal labs, but still aren't getting treatment.

So why does the free T4 stay relatively preserved in some patients?

The answer depends but usually is made clear by checking reverse T3 levels.

Remember that T4 is simply a reservoir hormone for T3.

T4 is inactive unless it is converted to T3.

But it can be turned into Reverse T3 instead of free T3 which can put the brakes on the thyroid and your metabolism.

But unless you check the reverse T3 level your free T4 may appear falsely "normal" despite the fact that your body is lacking thyroid hormone at the cellular level.

​You can read more about reverse T3 and how it impacts your body here

​Partial Thyroidectomy with Falsely "normal" TSH and T4/T3

This is another big one that I will occasionally run into and it just highlights how good the body is at preserving serum levels of thyroid hormone (or how inaccurate thyroid lab tests really are depending on how you look at it). 

Below is an example of a hypothyroid patient who underwent a partial thyroidectomy some 20+ years ago.

She was functioning with half a thyroid and yet her TSH was still 2.37 with a reference range of 0.45 to 4.5. ​

Thyroid resistance lab results

Despite that her labs look "decent" she was still suffering from many hypothyroid symptoms including: hair loss, weight gain, extreme fatigue, brain fog, etc. 

And it wasn't until she was started on naturethroid that she had near COMPLETE relief of all of her symptoms over a 6 month period and her body transformed in the process. 

In fact you can see her before/after pictures and case study here:

Melanie side view 9 month follow up

​So why is it that this patient was obviously hypothyroid, but she was still able to have "normal" thyroid lab tests?

​Again it highlights the importance of not focusing solely on the TSH but instead using other markers to help diagnose thyroid issues. 

If you take a look at her numbers you can clearly see that her free T3 is in the low end of normal and her reverse T3 is > 15 indicating she has a conversion problem.

When you understand how inflammation (indicated by her high CRP) leads to T4 to reverse T3 conversion, her thyroid labs make perfect sense.

But in order to come to this conclusion you really have to look at the whole picture. ​

thyroid metabolism reset poster for side bar

High TPO antibodies but Normal TSH with Hypothyroid Symptoms

​Then of course we have the situation of autoimmune thyroiditis...

The situation where patients have hypothyroid symptoms, "normal" lab tests but elevated antibodies to either Thyroglobulin or thyroid peroxidase.

Patients in this situation are often told to take the "sit and wait" approach.

That is sit and wait until your body destroys your thyroid gland from inflammation and autoimmunity and THEN you will need thyroid hormone.

​If the body is able to "preserve" thyroid function after a partial thyroidectomy (as evidenced above) then it is certainly able to preserve function if 10-50% of the thyroid gland is destroyed. 

This often leads patients with autoimmune thyroiditis until their TSH finally increases to a point where providers feel thyroid hormone is indicated.

​Obviously there is a better approach and that is to look and evaluate ALL thyroid laboratory tests (in addition to the TSH) and treat if there is a combination of symptoms + abnormal lab tests (even if those abnormal lab tests are just antibody levels). 

Below I've included an example from a recent patient who had undiagnosed autoimmune thyroiditis for many years:

High free T4 and low TSH in hashimoto's
elevated antibodies with high TSH

​You can see the TSH at 12.27 with a reference range of 0.40-4.50 in a patient with debilitating fatigue and weight gain for years (undiagnosed) with accompanying elevation in both thyroglobulin and TPO antibodies. 

​This is what will happen to your thyroid gland over time assuming you don't treat the autoimmunity or inflammation, and it just doesn't make sense to wait until the damage is > 50% to PROVE it. 

Changes in TSH over time and with disease severity

Why is it that in all of these conditions (they account for the majority of you guys reading this post by the way) the TSH and other lab tests remain decidedly "average" despite obvious dysfunction in other lab tests?

euthyroid sick syndrome lab values

​To better understand what is happening in your body it's best to visualize the thyroid lab tests overtime on a graph. 

Above you can see a graph which depicts all thyroid lab tests over time.

On the left is mild disease (inflammation, autoimmunity, chronic infection, dieting, etc.) and as you travel right on the X axis you can see how the lab tests change over time.

What's important here is that the TSH ​doesn't start to elevate until the disease state has reached "severe". 

Around this time is when the free T4 level also begins to drop as well below the "normal range".

​But compare those lab tests to both reverse T3 and free T3 which show changes MUCH earlier than the other lab tests, making these lab tests hold much more weight when determining if someone is truly hypothyroid. 

​This illustration helps explain (in addition to the differences in deiodinases, tissue level demands, etc.) why not all thyroid lab tests are created equal and why the TSH falls short if used by itself. 

Even if the TSH is used in tandem with free T4 it still misses the majority of cases until they are severe. ​

Instead one of the most sensitive ways to determine if tissues are getting enough thyroid hormone is the reverse T3 to free T3 ratio (which we will discuss below). ​

Conditions that make the TSH less reliable

In addition to the conditions listed above there are a few other states that make the TSH less reliable. 

I am talking about insulin and leptin resistance: ​

Leptin resistance and increased TSH

Both of these conditions reduce T4 to T4 conversion (studies showing this link for insulin resistance here, studies showing this link for leptin resistance here). 

In the most basic sense as leptin levels and insulin levels increase the body preferentially converts T4 to the inactive thyroid metabolite reverse T3.

This leads to an "adaptive" state which reduces metabolic energy expenditure.

In lay terms that means it reduces your metabolism.

The exact mechanism by which leptin and thyroid hormone are connected is not completely understood (you can read more about it here), but one thing is certain:

Leptin levels and thyroid function are connected. 

Leptin resistance and hypothyroidism both appear to be caused or sustained by caloric restricted diets (chronic yo-yo dieting) which causes high reverse T3 and low free T3 levels leading to clinical hypothyroidism.

The big problem is that this condition is not well recognized by many providers despite the fact that it is highlighted in medical literature (see links above). ​

  • Bottom line: If you have leptin resistance (as indicated by a high fasting leptin level) there is a VERY high chance you also have tissue level hypothyroidism even if you have "normal" lab tests. This condition may need to be diagnosed by testing both your reverse T3 and free T3 levels together. 

The Complete Thyroid Panel: How to Diagnose Hypothyroidism

​So let's say you are convinced that your thyroid is suboptimal and you'd like to prove it. 

What tests do you need and how do you interpret the results?

We are going to go over them below, but I need to say something first:

Thyroid lab tests shouldn't be used as THE definitive test for diagnosing and managing hypothyroidism by themselves.

They can be very helpful for the initial diagnosis and sometimes for management, but once you introduce thyroid hormone into the system exogenously (from the mouth) you have changed the dynamics of the system.

I'm not going to go into detail on this now, but just realize the lab tests aren't the end all be all for diagnosis.

Having said that they can be quite helpful, especially if you are thyroid hormone naive (meaning you haven't been on medication before).

If this is the case, then these ranges may be helpful for you:

  • Free T3: Should be in the top 50% of the reference range (may be falsely elevated in cases of high reverse T3)
  • Reverse T3: Should be < 15 (without exception), if your Free T3 is high and your reverse T3 is high then your ratio of T3 hormone in your medication is off
  • TSH: Should be < 2.0 *anything higher indicates tissue level hypothyroidism in other tissues in the body (note that a TSH < 1.0 does not indicate optimal thyroid function especially in the face of abnormal free T3 and reverse T3)
  • Total T3: Generally should be in the top 50% of the reference range
  • Free T4: Generally in the mid range (only useful if NOT on thyroid medication as high levels of T3 only hormone will drive the T4 down)
  • Sex hormone binding globulin: In women it should be in the 70-80 range and can be helpful for determining tissue levels of thyroid hormone (can't be used if a woman is on birth control medication or oral forms of hormone replacement therapy)
  • Thyroid antibodies: Should be < 30 (non existent for whatever reference range is used)
  • CRP and ESR: Both of these markers should be as low as possible (*note that these are non specific markers for inflammation and as they increase so to will the reverse T3)

​As you can see testing for hypothyroidism is far more complex than just testing the TSH (and maybe the free T4). 

When you understand the physiology and how difference aspects like inflammation, insulin resistance, and leptin resistance​ alter thyroid physiology it is easy to see how the TSH falls short. 

But remember:

Even those "optimal" reference ranges listed above can be misleading in certain cases, but if used in combination with hypothyroid symptoms (and occasionally basal body temperature + resting metabolic rate) you can really diagnose hypothyroidism. ​

I would also point out that these ranges are really only helpful for those NOT on thyroid medication already.

Once you start thyroid medication several changes take place that can artificially alter these numbers and make interpretation difficult unless you understand the physiology.

​As an example:

Increasing doses of Synthroid or Levothyroxine will certainly drop the TSH (remember there is no competition for reverse T3 in the pituitary) but may actually make thyroid function in the peripheral tissues worse due to T4 to reverse T3 conversion.

So lab tests in this instance would look something like this:

  • TSH decreases
  • Free T4 increases
  • Free T3 drops
  • Reverse T3 Increases
  • Sex hormone binding globulin stays the same indicating low tissue levels of thyroid hormone

​This pattern is seen very frequently in patients who are treated based off of the TSH alone but have insulin/leptin resistance and/or a history of calorie restricted dieting. 

If you call into that category you will need advanced thyroid testing and a provider who can interpret them for you.​

When is the TSH Helpful?

We just spent all this time discussing why the TSH doesn't provide very much value, but it turns out that it does have some limited value. 

TSH can actually be very helpful in initially diagnosing hypothyroidism and (sometimes) helping to determine dosing of thyroid medication. 


If your TSH is > 2.0 you are hypothyroid period. If you fall into this category you should be treated (or undergo a trial) of thyroid hormone. 

And Second: 

The rate at which your TSH drops can be helpful in determining your total dose of thyroid hormone needed.

Let's say you start with a TSH of 3.5. 

You start titration with Natural desiccated thyroid and after 2 months your TSH drops to 1.0 on 2 grains (130-135mg) of NDT.

This indicates your total dose will likely need to be much higher than someone who drops their TSH down to 0.05 with the same dose.

This highlights that each patient has a unique demand for thyroid hormone in their body and standard dosing should NOT apply to everyone.

It's also important to remember that BOTH T3 and T4 will cause your TSH to decrease.

In fact T3 thyroid hormone is 3x more potent at decreasing your TSH than T4 thyroid hormone, so put that into perspective when using medications like cytomel, liothyronine or NDT.

​So if you are started on any medication containing T3 and your TSH does not drop very quickly then that is an indication you might need higher doses of thyroid hormone. 

​Once you start treatment with thyroid hormone the TSH generally has less utility than the other thyroid lab tests indicated above, but it still can be useful under certain circumstances. 

Recap + What to do Next​

Let's wrap this long post up with a recap and some direction if you feel you fall into any of the categories listed above. 


TSH can be a helpful test but it really falls short under many circumstances in both the diagnosis and management of hypothyroidism. 

For several reasons (including pituitary sensitivity to thyroid hormone, hormone changes and differences in thyroid medication) measuring the TSH isn't the most accurate thyroid lab test. 

In fact, even with the combination of all thyroid lab tests sometimes diagnosis can still be difficult (meaning it must be based off of a combination of symptoms and lab tests). 

In cases of low T3, subclinical hypothyroidism, partial thyroidectomy and autoimmune thyroiditis the TSH may NOT accurately reflect the thyroid status of your body. 

If you feel that your TSH doesn't reflect your thyroid status then your best step is to look for a knowledgeable provider to order ALL of the tests necessary for diagnosis. 

Generally this means you will have to look outside of the insurance model (I know it's not what you want to hear but it's just the truth right now) because most Doctors practice what is known as the "standard of care" and that standard is to test only the TSH. 

If you are working with someone and they don't order the tests, or balk when you ask for certain tests that is a good indication they are not the provider for you. 

No matter how hard you try you will never be able to "force" your doctor to listen or order the right tests - so don't waste your time. 

Find someone who can help you. 

Now it's your turn:

Do you feel the TSH has been helpful in diagnosing or managing your thyroid condition? 

Why or why not?

Leave a comment below! 

Westin Childs

I'm Dr. Childs and I write these posts. I'm a physician who specializes in helping people lose weight, have more energy and FEEL better. My practice focuses on hormone imbalances, thyroid issues, and weight loss resistance. My goal is to provide the BEST information out there on the internet that is both actionable and trustworthy. Get my free 3 day meal plan here. You can also find more about my personal journey back to health here.

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