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Elk River Chiropractor | Elk River chiropractic care | MN | Free T3

           Dr. John Larson & Dr. Jennifer Dahlseid                 Phone:  763-241-5436

          200 5th Street NW                                                            Fax: 763-241-5466

          Elk River, MN  55330                                    service@HealingChoices.com

Free T3
Elk River Chiropractor | Elk River chiropractic Free T3 |  MN |

Thyroid Lab Tests:

The Power of Testing

Free T3


Free T3 is one of our 6 Critical Thyroid Lab Tests.  (To see a list of all 6 click here.)  Testing Free T3 is easily one of the most important measures of the amount of thyroid hormone in your body.  Ironically, it is often NOT tested by medical providers as part of a screening test for thyroid function, and many people are told their thyroid is "normal" . . . when a simple lab test for Free T3 would reveal it is not normal.

What is T3 and why is testing Free T3 so important?

T3 is one of the many forms of thyroid hormone in your body.  When your thyroid gland is stimulated to produce thyroid hormone . . . your thyroid gland produces mostly the form of thyroid hormone we call T4 and very little T3.  It is called T3 because there are 3 iodine molecules attached to the hormone complex.

Your thyroid produces far more T4 than T3 in about a 20 to 1 ratio . . . meaning 20 particles of T4 hormone for every 1 particle of T3 hormone.  The problem with relying on T4 as a measure of the amount of thyroid hormone in your body is that T4 has less biological activity compared to the more bio-available form of thyroid hormone we call T3.  This means that T4 has less effect in stimulating the metabolism of your cells, and less effect on determining the metabolism of your entire body.  T3 is the bio-available or more active form of thyroid hormone, and it's the Free T3 that is communicating to your cells and determining your energy production, energy levels, and your overall metabolism.

T3 - like most hormones in your body - exists in both a bound (inactive) form, and an unbound (active) form.  When a lab test is measuring the Total T3 levels it is measuring the total of inactive + active forms of T3.  Because your body can only use a hormone when it is available in the unbound (active) form . . . what we also call the "Free" form . . . it is far more useful to know the levels of the active (Free) form of a hormone . . . this makes Free T3 the best measure of T3 levels.

How does Free T3 actually determine your metabolism - what is the mechanism?

Some of you may have heard of this very small part of all your cells called the mitochondria . . . also known as the "powerhouse" of your cell because this is where your cell produces the energy it needs to function.  This "molecule of energy" is often called ATP.  Some cells in your body may only have a few mitochondria, and other cells that require more energy - like your muscle cells - may have hundreds of mitochondria in a single cell.  The number and health of your mitochondira determines the metabolism of each cell . . . and the sum total of all the mitochondria in all the cells of your body determines the metabolism of your entire body.

Why do we care about these things called mitochondria and Free T3?  Your mitochondria - as the energy producers of your cell - receive their instructions on how much energy to produce from your thyroid hormone.  And it's not just any form of thyroid hormone . . . it is specifically the Free T3 that communicates with your mitochondria and has the greatest impact for controlling energy production and your overall metabolism.

What else is important to have healthy T3 levels?

As we mentioned above . . . your thyroid produces mostly T4 and very little T3 . . . and T4 has much less ability to stimulate your metabolism compared to the highly active T3 form of thyroid hormone.  So where then does this T3 come from?

T3 is created in your body by converting or changing T4 into T3.  About 80% if this conversion of thyroid hormone (T4) into its more biologically active form (T3) takes place within your liver.  This means that a healthy functioning liver is necessary for healthy thyroid hormone levels, and for creating enough T3 for you have good evergy levels and a good metabolism.

Another important factor is nutrient called selenium.  Selenium is a critical nutrient necessary for proper conversion of T4 into T3, and a deficiency of selenium in the body, or lack of selenium in the diet, could limit the amount of T3 that gets created.

This means that both healthy liver function and enough selenium are critical for having healthy levels of the most active form of thyroid hormone - called Free T3.  When people test with normal T4 levels in blood testing, but they are low in T3 levels . . . we refer to them as being "poor converters" . . . meaning their body is doing a poor job of converting T4 into T3, and we become more concerned that a selenium deficiency and/or a liver problem that is contributing to their thyroid problem.

What does the Free T3 lab result mean?

Let's first take a look at the reference ranges for this lab test.  Keep in mind these reference ranges many vary slightly from one lab to another, and the reference ranges shown below are in Standard U.S. Units (not Standard International Units) but a common range provided by the lab will look like this:

Free T3 (Triiodothyronine, Free):  2.0 - 4.4

Also keep in mind that most labs will provide a reference range on their lab report that is very wide range, and does not represent what is actually considered an optimal level indicating the best function of your thyroid.  A more critical evaluation of the Free T3 lab test will look like this:







Looking at a lab result for more than what is simply a Clinical High or Clinical Low result is referred to as "Functional Lab Testing".  This requires one to consider what is truly an Optimal range . . . meaning it is the best range for Free T3 to be in for optimal thyroid function.  It also considers a Functional High and Functional Low range . . . meaning it is starting to move in the wrong direction and a person is likely starting to feel some symptoms of poor thyroid function even though it is not yet in the clinical high or low range.  Here's what you want to be thinking about for each of these reference ranges:

Free T3 at Clinical High (4.5 or higher)This indicates an obvious overactive or hyperthroid function (hyperthyroidism) and there is likely too much thyroid hormone in your system to be healthy.  With Free T3 in the Clinical High range a person would likely receive a clinical diagnosis of Hyperthyroidism.  Usually this is in response to taking a thyroid medication dose that is too high, or the thyroid has become overactive in response to an auto-immune condition . . . but could be due to other problems as well.  If an auto-immune thyroid condition is discovered, then the goal is to reduce the auto-immune reaction using dietary and nutritional strategies - which can be very effective.  If a medication dose is too high, then the prescribing doctor will need to reduce the daily dose of the medication.

Free T3 at Functional High (3.9 - 4.4)While many health providers will dismiss this as being within the labs reference range of "normal".  The reality is that some people may be suffering with the symptoms of an overactive or hyperthyroid function when their Free T3 levels are testing in this range, but this sould first be compared to other thyroid lab test   Free T3 will often be in this range for two reasons:  1) they are on a thyroid medication and their medication dose is just a little too high, or 2) their thyroid function is starting to go into overdrive - often in response to an auto-iummune condition which can be confirmed by testing the thyroid antibodies in lab testing (Thyroid Peroxidase Antibody or TPO and Thyroglobulin Antibody).  If an auto-immune thyroid condition is discovered, then the goal is to reduce the auto-immune reaciton using dietary and nutritional strategies - which can be very effective.  If a medication dose is too high, then the prescribing doctor will need to reduce the daily dose of the medication.

Free T3 at Optimal (2.8 - 3.8):  This is considered the optimal range for Free T3 indicating you have the best or optimal function of your thyroid.  Keep in mind that what is considered the Optimal range may vary slightly when you are working with a doctor that specializes in Functional Lab Testing.  This slight difference of opinion on what the Optimal range should be is often based on the differences in the experience and training that doctors receive over their years of helping people, but the Optimal range among all Functional Medicine Doctors is likely near the suggested range shown here of 2.8 - 3.8.

Free T3 at Functional Low (2.0 - 2.7)While many health providers will dismiss this as being within the labs reference range of "normal".  The reality is that many people are suffering with the symptoms of low thryoid function when their Free T3 levels are testing in this range.  I will often tell my patients to think of this as a "pre-hypothyroid" range.  Just like a person can be pre-diabetic . . . you will want to take action and make changes before they become a full diabetic.  The same is true of your thyroid . . . many people are pre-hypothyroid and we want to take action to improve this before it gets worse and becomes a full hypo-thyroid condition.  I have seen with my own patients that the right natural or nutritional therapies can work very well to improve thyroid function when the Free T3 is in the Functional High range, and will often bring the Free T3 lab test back into the optimal range.

Free T3 at Clinical Low (0.0 - 1.9)This indicates an obvious low throid function (hypothyroidism) and there is likley not enough thyroid hormone in your system to be healthy.  With Free T3 in the Clinical Low range a person would likely receive a clinical diagnosis of Hypothyroidism, and then be prescribed some type of thyroid medication from their medical provider.  Keep in mind that there are many things that can be done from a natural or nutritional prespective that can help improve how your own thyroid gland is functioning.  It may not eliminate the need for a thryoid medication, but it can reduce your dependence on this medication by helping your own thyroid function the best it can.  If you are already on thyroid medication then your medication dose is too low, or you may do better on a different thyroid medication.

In summary . . .  keep in mind that Free T3 is the more important lab test to determine the amount of thyroid hormone that is having the greatest impact on your energy levels and your metabolism, but you still want to be testing T4 as well.  If T4 is normal and T3 is low . . . then you have a "conversion problem".  This means your body is not converting T4 into T3 as efficiently as it should be, and this could be due to poor liver function and/or a selenium deficiency.

I'm sure there are other people you know who would benefit from reading this information.  There will be many more articles coming in the future on all aspects of thyroid function, and what factors will help or harm your thyroid function.  Be sure to share this information with family and friends who have been diagnosed with a thyroid problem, or the people you care about who are suffering with symptoms of a thyroid problem.  The rest of the information on the 6 Critical Thyroid Lab Test will be coming soon!

Your partner in Health and Happiness,

Dr. John W. Larson, DC

Clinical Nutrition and Hormone Health Expert




Elk River Chiropractor | Free T3. Dr. John Larson is a Elk River Chiropractor.
Healing Choices - Natural Healthcare     200 Fifth Street NW     Elk River, MN  55330  
Phone: (763) 241-5436     Fax: (763) 241-5466     Email:  service@HealingChoices.com

Disclaimer:  This information has not been evaluated by the Food and Drug Administration.  The information should be considered opinion and for educational purposes only.  Nothing on this webpage or website is intended to diagnose, treat, cure or prevent any disease.