understanding thyroid hormone blood test results

Understanding your thyroid hormone blood test results

In this article we look at interpreting your thyroid hormone blood test results. To do this I break down each individual marker, what it is and why it is tested. Throughout the article we discuss the potential imbalances or patterns that you may see.

Not sure if you have a thyroid issue? Well the first step might be understanding the signs and symptoms. Click to read my article ‘Why the thyroid is important and what symptoms, imbalances and testing options you should be aware of.

What thyroid markers should I get tested?

I touched on this in the previous article linked above, not all are always necessary, in fact TSH, Free T4 and Free T3 are a great start and already gives a lot more info than just TSH alone which is the most common assessment.

If dysfunction is noted with TSH, Free T4 and Free T3, then a broader blood test should be recommended, including some or all of the markers below.

Markers discussed in this article:

  • Thyroid Stimulating Hormone (TSH)
  • Total T4/Thyroxine (T4)
  • Total T3/Triiodothyronine (T3)
  • Free T4/Free Thyroxine
  • Free T3/ Free Triiodothyronine
  • Thyroid Peroxidase (TPO)
  • Anti-thyroglobulin Antibody (TG)
  • T3 Uptake
  • Reverse T3

Please note that many medications & being pregnant can influence the test results, so these should be considered prior to the blood test.

Understanding your thyroid blood markers

Thyroid Stimulating Hormone (TSH)

This is the hormone produced by the pituitary gland in the brain. This marker alone helps to indicate if the thyroid is under or over active. When levels of TSH are very low, this should be a result of high levels of circulating thyroid hormone, in particular thyroid hormone T4. This is because the pituitary responds to the levels of T4 in the body and upregulates or down regulates TSH in response to send a message to the thyroid gland to make more or less thyroid hormone.

So, typical patterns should be:

  • Normal TSH & Normal Free T4 – Normal thyroid
  • Low TSH & High Free T4 – Hyperthyroidism or perhaps excessive thyroxine medication
  • High TSH & Low Free T4 – Hypothyroidism

Wouldn’t life be wonderful if the human body followed these predictable patterns. Well unfortunately that is not always the case, in fact the most common patterns that I see are as follows:

  • Low or Normal TSH and Low Free T4 – Low functioning pituitary function or impaired feedback to the brain about thyroid hormone status.
  • Normal TSH, Normal Free T4 but low Free T3 – Poor conversion of T4 to T3 or excessive conversion to inactive forms of thyroid hormone such as reverse T3. Ultimately though it will still cause low thyroid symptoms if free T3 is low.

The challenge with the above two patterns is that conventionally, these imbalances are rarely recognised as dysfunctions that merit support. For those with more ongoing chronic health complaints these imbalances can, in my opinion be more common than the classic primary hypo/hyperthyroid imbalances that I mentioned previously.

Low TSH levels when Free T4 and Free T3 are low warrants further investigation into areas such as immune imbalances, oxidative stress and inflammatory imbalances, neurotransmitter imbalances, prolactin levels and stress are warranted to help address the underlying cause.

Total Thyroxine (T4)

Your thyroid produces around 93% thyroid hormone T4. This hormone supports several functions including growth, foetal development, metabolism etc. Total T4 looks at the combination of Free T4 and the T4 that is also bound to something called Thyroid Binding Globulin (TBG), a type of protein that helps to bind the thyroid hormone and transport it around the body.

Total T4 is a good indication of the total amount of T4 produced by the thyroid gland, however the total amount is not always a good indicator of whether you will have thyroid symptoms. For example, if too much is being bound up by high levels of TBG then you can see low levels of free T4. It is therefore imperative that Free T4 is ran alongside this. Alternatively, if you had to choose, then run Free T4 only and drop total T4.

Elevated T4 levels can be influenced by medications, excessive iodine, certain diseases, autoimmunity, cancers and excessive levels of TBG.

Very low levels are typically seen in primary hypothyroidism, chronic dietary/calorie restriction and nutrient deficiencies, autoimmunity or pituitary dysfunction – Excessive TSH production even when T4 levels are high/normal.

Free Thyroxine (Free T4)

As mentioned above, this marker provides what the levels of available free T4 are. Remember it is the free hormone that is able to act upon our cells and influence our physiology.

High Free T4 can lead to a hyperthyroid state and low Free T4 can lead to a hypothyroid state. I discuss symptoms of high and low thyroid hormones in the previous article.

When Free T4 levels are low you must look to find out why. Considerations include the following:

  • Not enough T4 being produced by the thyroid gland – thyroid hormone production issue. Could be related to nutrient insufficiencies (A, D, Zinc, Selenium, Iodine etc), low progesterone in females effecting thyroid peroxidase activity, imbalanced blood glucose etc.
  • Thyroid gland not getting the message to make thyroid hormone (low TSH causing a production issue) – Pituitary issue.
  • Excessive T4 bound to TBG – Binding Issue.
  • Excessive T4 being converted to other thyroid hormones – Conversion issue.

Total & Free Triiodothyronine (Total T3 & Free T3)

As mentioned above the majority of thyroid hormone produced by the thyroid gland is T4, whereas around 7% is T3. Most T3 is produced in the liver, gut and other tissues via conversion from T4 to T3. The majority of that conversion takes place in the liver (roughly 60%), then the gut and other tissues for the remainder.

T3 is crucial for many functions in the body including growth, body temperature, heart rate etc. It has a significant stimulatory effect on your cells function and therefore when levels are low a wide arrange of symptoms can develop. Typically, symptoms are associated with a slowing of cellular function, therefore weight gain, low energy, poor wound healing and reduced quality of hair, skin and nails etc can develop.

As with T4, TBG can bind up T3 meaning it is not available to exert its response on your cells. As a result, someone can have normal/high total T3 but if their Free T3 is low they will still have low thyroid symptoms.

Common patterns I see where T3 is an issue include:

  • Low Free T3 and normal Free T4 and TSH – poor conversion or excessive conversion into the inactive form reverse T3.
  • Low Free T3, Low Free T4, High TSH – Primary hypothyroid.
  • Low Free T3, Low Free T4, Normal/High TSH, Normal Total T4 & T3 – Binding issues/excessive TBG.

Free T3 is not a common marker to be ran in conventional settings. Normally just TSH or TSH and Free T4 are ran to assess thyroid function normally. Assumptions are made that if Free T4 is normal then T3 must also be normal, this can be a false assumption, especially in those with classic hypothyroid symptoms but “normal” blood test results (TSH & Free T4).

T3 is rarely used as a medication because it is very fast acting and brings with it an increased risk of side effects. Instead T4 is used and conversion is assumed. Whether you suspect you have low thyroid issues, or you are taking thyroid medications to manage a thyroid issue, you should be assessing Free T3 levels.

A common group that I see low T3 levels in are people that have been chronically restricting their calories comparative to their expenditure. Often with these individuals slowly increasing their calorie intake is needed to help correct T3 levels again. These are the individuals who on paper should be losing weight because of the apparent deficit in energy but are no longer losing weight/fat, instead feel tired and sluggish, perhaps have issues with their menstrual cycle, feel water retentive and heavy, reduced hair skin and nail health etc. Often, these individuals find themselves being accused of mismanaging their calories and they just need to eat less and do more, this is far from the truth and this often exacerbates the vicious cycle creates a lot of mental/emotional stress and upset.

The conversion of T4 to T3 relies upon a healthy liver, gut and more. It is also influenced by inflammation & stress levels, hence when trying to correct a low T3 state there are multiple areas of consideration.

Thyroid Peroxidase Antibodies (TPOAb) and Anti-Thyroglobin Antibodies (TGAb)

These markers are associated to autoimmune thyroid disease. Autoimmune thyroid disease occurs when cellular damage takes place on specific thyroid tissues, eventually impacting the proper function of that gland and resulting in changes in thyroid hormone production. Ultimately this is when an individual’s immune system mistakenly recognises thyroid tissue as foreign, leading to chronic inflammation and immune response against that tissue.

When hyperthyroid is suspected TSH receptor autoantibodies (TRAb) may be assessed as it can mimic the action of TSH and lead to excessive production of thyroid hormones. If this is present then this is often the cause of Hyperthyroidism, Grave’s Disease. This usually requires immediate acute intervention and then ongoing support to try and determine what has caused the immune system imbalance, otherwise lengthily use of immunosuppressants may be recommended.

In the case of hypothyroid, then we tend to look at TPO and TG. TPO antibodies are involved in the tissue destructive process associated with hypothyroid Hashimoto’s. Often TPO levels are elevated with normal TSH, T4 and T3 levels, however it can be a bit of a ticking time bomb and often you will see a progression towards Hashimoto’s over time, if nothing is done to manage the immune imbalance.

TPO antibodies are more common than TGAb and more indicative of thyroid disease. However, the production of TGAbs can induce a massive destruction of the thyroid gland.

Autoimmune thyroid Hashimoto’s is the most common cause of hypothyroidism, although many people never have these markers assessed and are just placed on thyroxine to manage the low thyroid levels and just treated as primary hypothyroid patients. This typically does nothing to slow or stop the destruction that led to hypothyroidism in the first place. Ultimately what you are looking at is an immune issue and not a thyroid issue. This is not to say the thyroid shouldn’t be treated, it will most certainly need to be treated in some way or another, however, we must look to understand the underlying cause of the development of the hypothyroidism in the first place. In doing so, you can avoid further issues or increased reliance on thyroid medication.

T3 Uptake

T3 Uptake has nothing to do with actual T3 levels. It is used to help determine the levels of Thyroid Binding Globulin because it’s measurement reflects the available binding sited for thyroid hormone. As we have discussed previously, excessive binding protein can result in low levels of Free T4 and Free T3, meaning there is less available to create it’s biological effect on our cells.

Elevated levels of estrogen for example can increase levels of TBG, whereas elevated testosterone can actually lead to a decrease in TBG. Unfortunately, this marker can be skewed by a number of things, including certain medications, illnesses, salicylates, pregnancy, contraceptive medication use etc.

Reverse T3

Reverse T3 (rT3) is the measure of the amount of reverse T3 produced from T4. This is the inactive form of thyroid hormone T3. rT3 seems to increase during times of extreme stress, both acute such as trauma or chronic stress such as more mental and emotional stressors or even chronic calorie restriction, perhaps as a protective mechanism for survival.

High production of this inactive form of T3 can compete with free T3 at a cellular level. Meaning it can potentially contribute to a low thyroid hormone state when elevated and enough free T3 is displaced from the cell receptor.

Having some rT3 is totally normal, so it is about looking at the full picture and consider how much the rT3 levels might be impacting thyroid symptoms.

Normal vs Optimal Reference Ranges

The is a very important concept to think about. Normal levels are established to determine if there is a diagnosable condition/disease present.

Optimal reference ranges are established by looking at what the best range is for health or what provides the lowest risk of mortality. Just because one is slightly out of optimal ranges does not mean it requires action. Action is based upon the bigger picture (other test results, symptoms etc) and looking for trends in test results.

There will be variations in normal reference ranges based upon the lab used but should be around the same ball park figure. Optimal ranges are a little more controversial as the data for these optimal reference ranges is not something that has been clinically defined in many cases.

When looking at test results it is crucial to look at both the normal levels (are you free from disease or a diagnosable condition that might require acute support) and optimal levels with symptom assessment (are you as good as you could be and therefore choosing an appropriate intervention).

Summary of imbalances leading to a low functioning thyroid state

Firstly, choose an appropriate lab test, the more thorough the test, the better placed you will be to understand where the dysfunction is coming from and therefore the better placed you are to come up with an appropriate plan of action.

Below are certain imbalances that can develop and consider what you can do about them.


WHY – It’s not sending the message to the thyroid to make adequate thyroid hormone. Could be low TSH because of pituitary suppression or could be low Thyrotropin Releasing Hormone (TRH) production from the hypothalamus in the brain thus not sending the message to make TSH.

WHAT YOU CAN DO – Check for high stress, inflammation, infection or consider further pituitary assessments.


WHY – May be struggling to produce thyroid hormone.

WHAT YOU CAN DO – Check for nutrient insufficiencies such as selenium, tyrosine, iodine, iron, zinc etc. Can also check for toxin exposure, hormone imbalances (low progesterone in females) that could effect thyroid peroxidase levels.


WHY – Too much is being bound up, thus impacting healthy thyroid hormone levels.

WHAT YOU CAN DO – Check for liver issues, hormone issues, excessive estrogen or estrogenic chemical exposure, acute trauma or chronic stress.


WHY – Perhaps the immune system is impacting the production of thyroid hormone levels through an autoimmune reaction.

WHAT YOU CAN DO – run thyroid antibodies such as TPOAb and TGAb.


WHY – Is there inadequate conversion from T4 to T3 or excessive conversion from T4 to reverse T3 resulting in low thyroid hormone T3 and therefore low thyroid symptoms?

WHAT YOU CAN DO – Evaluate stress, inflammation, nutrient deficiencies like selenium, liver issues, digestive issues, sex hormone imbalances.

Cellular function

WHY – Not one I have touched above as it cannot be tested. However, there can be issues with thyroid hormone being able to enter the cell to cause its metabolic effect.

WHAT YOU CAN DO – Inflammation, high stress, elevated homocysteine, vitamin A deficiency are all considerations.

You can see from the above that when looking for true underlying cause to your thyroid imbalance, more than just the thyroid gland and thyroid hormones themselves have to be taken into consideration. Nutrients, stress, other hormones, liver function, medications, exercise, diet history, chemical exposure, autoimmunity can all impact thyroid. Your journey is likely to be unique and deserves an individualised approach rather than the same old way of managing thyroid health that has been about for years. This is not to say abandon conventional approaches, in some cases this is the best method of management and is required, however in almost all cases this ignores underlying cause.

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