Thyroid Lab Tests: A View From the Inside



Thyroid lab tests are the general standard for measuring function and to determine what is or is not working. While these tests can be very effective in helping you discover where the problem might be, they are not perfect. And for those people with Hashimoto’s they can be misleading.

This is simply because all your thyroid numbers may look fine, but you still feel may like crap. Laboratory tests of thyroid function do not account for flare ups and do not really tell you anything about how your immune system is functioning. In a future post, we will take a look at how to better assess your immune system.

Why Do I Still Have Symptoms Even Though My Thyroid Lab Tests Are Normal?

The way the thyroid works in the body is kind of like a bucket brigade. Hormones pass the tiny bucket from the brain, to the pituitary gland, to the thyroid gland, to the liver, and finally to the cells of the body.

The body sends a message to the brain and says “Let’s pick it up!” or “Slow your roll!” (speed up or slow down the metabolism). The part of the body that receives this message is the hypothalamus. The hypothalamus delivers the message to the pituitary gland using thyrotropin releasing hormone (TRH). The brain secretes thyroid stimulating hormone (TSH) which tells the thyroid to make and secrete T4 and T3.

The body can only use T3 and only 7% of it comes from the thyroid gland. The body has to convert the rest from T4. This happens in the liver, the gastrointestinal tract, and in other parts of the body like muscles, the heart, and nerve cells.

So, if your liver isn’t working properly or you have gastrointestinal issues like leaky gut or unhealthy gut flora (bacteria), or your pituitary gland is tired, or you have too many thyroid binding proteins in your blood from too much estrogen or you have an immune problem, you can wind up feeling lousy. It is not uncommon for people to have more than one of these issues at the same time.

And your test results might look perfect. In my last post I discussed how systems of the body are affected by the thyroid. Here you can see how the opposite is also true. All of these systems affect how the thyroid works.

With Hashimoto’s, a lot of what may be causing your symptoms is an autoimmune attack on different tissues of your body. Often, people with autoimmune disease have multiple tissues being attacked and this has less to do with the thyroid than with the immune system.

TSH, The Standard That No One Can Agree On

Typical Lab range: (see below)

Functional range: 1.8 -3.0 mU/L

Thyroid stimulating hormone (TSH), also called thyrotropin is released by the pituitary gland after the hypothalamus releases TRH (thyrotropin releasing hormone). TSH is the most common and most sensitive marker used to assess thyroid function.

Many laboratories have now taken to doing what is called a “thyroid cascade” in order to save themselves and insurance companies money. Basically, if the TSH is deemed to be in the normal range they will not analyze for T3 or T4 or anything else. The problem is, there isn’t a lot of agreement about what the “normal range” is.

Since 2003, the American Association of Clinical Endocrinologists has recommended that the normal range run from 0.3 to 3.0, versus the older range of 0.5 to 5.5. So, according to the new standards, levels above 3.0 are evidence of possible hypothyroidism, and levels below 0.3 are evidence of possible hyperthyroidism. However, there is disagreement among practitioners, and some follow the older range, others use the newer range.

An important thing to understand about TSH is that it is an inverse number when thinking about thyroid function. The higher it is, the more sluggish, under achieving and, generally, slow your thyroid is. The lower it is, the more hyperactive, overachieving and, generally doing too much your thyroid is. Put another way: High TSH = hypothyroid, Low TSH = hyperthyroid.

TSH levels increase as T4 levels drop and TSH levels decrease as T4 levels rise. The reason this is the most popular test in today’s medical model is because the only treatment offered for thyroid dysfunction is thyroid hormone replacement and that’s what doctors are checking when they test your TSH.

A TSH test alone doesn’t give you information about thyroid pituitary communication, about T4 to T3 conversion in other parts of the body or about whether or not your immune system is attacking your thyroid. One important thing for Hashimoto’s people to understand is that some antibodies can inhibit thyroid function by turning off instead of stimulating TSH receptors on cells. In this case, you will see high TSH and high antibodies.

Bottom Line on TSH

Laboratory range is somewhere between 0.3 (to 3.0) and (0.5 to) 5.5. That is a huge range and borders on the ridiculous. The lab range values are made based on the general population that goes to the lab.

Most people who go to the lab are taking thyroid hormones or are poorly managed or completely undiagnosed (or all of the above) so this is not really a good measure of optimal thyroid health. Practitioners of functional medicine (like yours truly) look at a narrower range that we and some endocrinologists believe is a much better range for assessing a healthy thyroid.

This range is: 1.8 to 3.0. Notice it is higher on the low end and equal to or lower on the high end. Less is more, people, when comes to monitoring a healthy thyroid.

Total Thyroxine, (TT4)

Typical lab range: 5.4 – 11.5 ug/d

Functional range: 6-12 ug/d

The TT4 test measures both bound and unbound thyroxine levels and is not a good marker for T4 activity when measured alone. Total T4 is increased with lower TSH and is decreased with higher TSH. It is decreased with low TSH when the pituitary gland is not functioning properly (pituitary hypofunction).

Many drugs can alter total T4 levels. In my book Roadmap to Remission I explore these interactions.

Free T4

Typical lab range: 0.7 – 1.53 ng/dl

Functional range: 1.0 – 1.5 ng/dl

Free T4 is used to measure the amount of free or active T4 in the blood. High with hyperthyroidism, low with hypothyroidism. The drug Heparin can also cause elevated free T4 as can some acute illness. Its also high in an overdose of thyroid hormone.

Free Thyroxine Index (FTI)

Typical lab range: 4.6 – 10.9 mg/dl

Functional range: 1.2 – 4.9 mg/dl

On its own, this test is pretty useless. Total T4 and T3 Uptake are both used to calculate this marker (TT4 x T3 Uptake = FTI). Prescription drugs often affect T4 and resin T3 uptake levels in opposite ways (if T4 goes up resin T3 uptake goes down and visa versa). Many of these drugs affect thyroid hormone binding sites on cells. FTI is increased in thyroid hyperfunction and decreased in thyroid hypofunction and when your body needs selenium.

Total Triiodothyronine (TT3)

Typical lab range: 60-181 ng/dl

Functional range: 100 – 180 ng/dl

Total T3 gives you the total concentration of T3 in the blood. It is the preferred test for thyrotoxicosis (hyperthyroid condition, like Graves disease). Total T3 can also be useful in identifying problems of conversion from T4 to T3 in body tissue involving the enzyme 5′-deodinase.

This enzyme both converts T4 to T3 and stops T4 from working in the body.

Resin T3 Uptake

Typical lab range: 24 – 39 md/dl

Functional range: 28 – 38  md/dl

This test measures the amount of sites for unbound T3 to bind on thyroxine-binding proteins. Many medications can cause high or low resin T3 uptake. In my program Healing Hashimoto’s: The 5 Elements of Thyroid Health we explore these interactions. Elevated testosterone or testosterone replacement therapy can reduce the number of these binding sites.

This causes a low T4 measurement because it leaves very few binding sites for thyroid hormone to attach to. In contrast, anything that raises the number of binding sites, like estrogen or birth control pills will cause a pattern of high total T4 and low T3 uptake.

To summarize, T3 uptake is increased with hyperthyroid and with high testosterone. T3 uptake is decreased with hypothyroid and high estrogen levels.

Free Triiodothyronine (fT3)

Typical lab range: 2.30 – 4.20 pg/ml

Functional range: 3.0 – 4.0 pg/ml

This test measures the free T3 hormone levels. This test is rarely ordered by traditional endocrinologists and is usually only used when a patient has hyperthyroid symptoms and the fT4 levels are normal.

Even so, this test can be really useful for finding out what amount of active thyroid hormones are available for the thyroid receptor sites. Free T3 is high in hyperthyroid conditions and low in hypothyroid conditions.

Reverse T3 (rT3)

Typical lab range: 90 – 350 pg/ml

Functional range: 90 – 350 pg/ml 

This test measures the amount of reverse T3 that is produced (duh!). Reverse T3 is usually produced when there is an extreme amount of stress. For example, a serious car accident, or surgery or really bad chronic stress.

Its no surprise that this is elevated after a stress response or when the body produces high amounts of the stress hormone cortisol. Reverse T3 is low when you have severe tissue damage like a bad burn or laceration or when you have liver disease like cirrhosis.

Thyroid-Binding Globulin (TBG)

Typical lab range: 15 – 30 ug/dl

Functional range: 18 – 27 ug/dl 

Thyroid-binding globulin binds thyroid hormones that are circulating throughout the body. It is the main protein for carrying both T4 and T3 in the blood. This test may help determine thyroid problems from things not directly related to the thyroid like drugs, liver disease, infection, stress from surgery, etc.

Many drugs can alter TBG levels. In my book Roadmap to Remission I explore these interactions.

Thyroid Antibodies

Typical lab range for all antibodies: Above the laboratory range

When these antibodies are present, it means that your immune system is attacking your own tissue. When your body produces thyroid autoantibodies it could create a hypo- or hyper- thyroid state. They may also be elevated if there is thyroid cancer. Some antibodies can attach to TSH receptors, but they don’t cause a response in the thyroid.

These people will complain of low thyroid symptoms, but the TSH might not change at all. In other cases, the antibodies bind to receptor sites and cause the thyroid to be over active. Here you will see high T4, low TSH and high antibodies.

There are 3 autoantibodies that are tested. The first 2 are the most common:

Thyroid Peroxidase Antibody (TPO Ab): This antibody is the one that is usually high in autoimmune thyroid conditions like Hashimoto’s. It is also known as microsomal antibody.

Thyroglobulin Antibodies (TgAb): These aren’t seen high as often as TPO Ab. They are usually ordered when thyroid lab results seem strange because these antibodies can interfere with thyroid hormone production. TgAb is also used to monitor progress after surgery for removing the thyroid in thyroid cancer.

Thyroid-Stimulating Hormone Receptor Antibody (TRAb): This antibody is only ordered when a patient is hyperthyroid. Positive results usually mean Grave’s disease.

If Your Antibodies Are High Should You Retest Them to Monitor Progress?

Once you have tested antibodies and they are high, you have established that you have Hashimoto’s. Of course, these should be looked at in the context of other tests to determine how your thyroid is functioning.

Testing antibodies again is not that helpful for patients with Hashimoto’s because antibody levels can change throughout the day and may rise and fall without giving you any real relevant information about how well you are managing your disease.

They are also not a god indication of how your immune system is doing.

Antibody levels getting higher is not necessarily a bad thing, it can be an indication that treatment has stimulated a certain aspect of your immune system.

And antibody levels going down is not automatically a good thing, it may not lead to any improvement in symptoms.

How Can I Order These Tests If My Doctor Only Orders TSH?

The reality of having Hashimoto’s is that, in many cases, you have to take matters into your own hands to get proper care. This condition is one of the most poorly managed conditions in healthcare today. This is certainly true with lab tests.

The best thing to do is to work with a practitioner who knows what they are doing and who can order tests to properly assess you thyroid. This way and you can know if what you are doing is working or not.

Be prepared that you may have to come out of pocket to pay for these tests yourself if your doctor or your insurance company don’t deem them medically necessary.

The good news is that laboratory tests have become much more affordable and some functional medicine practitioners, like myself, pass this savings onto their patients because we believe you shouldn’t go broke to get better.

Final Thought

Interested in learning more? Check out this post for a more complete overview of lab tests fro Hashimoto’s.

Hashimoto’s is a thyroid condition and an autoimmune condition, both issues must be addressed to successfully manage this condition. Please let me know your thoughts and questions, I’d love to hear from you.


Mastering the Thyroid, 2011, Kharrazian, Datis, DC



About the Author Marc Ryan

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