Top 10 Thyroid Tests and How to Interpret Them

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Note: Originally published in February 2015, this article has been revised and updated for accuracy and thoroughness.

Many cases of thyroid problems are missed because most doctors don’t perform a comprehensive test panel. I spent almost a decade undiagnosed because I only had one marker tested and my thyroid diagnosis was missed completely, leading me to deal with needless symptoms like chronic fatigue, depression, anxiety, and many others for far too long!

If you suspect that you may have a thyroid condition, or know someone who does, this article will go over all of the most helpful tests that can help you identify a thyroid condition.

This article will also teach you how to understand your labs so that you can advocate for proper treatment for yourself.

If your doctor is ordering these labs for you, be sure to request a copy of your thyroid labs so that you can see them for yourself and ensure that they are interpreted correctly.

Additionally, I am including self-order options for most of the labs discussed, in case your current doctor won’t order the labs for you, or if you have a high insurance deductible.

The self-order options are discounted panels that I set up with Ulta Lab and can be ordered anywhere in the US. You will receive a lab order that can be taken to your local lab, and the results will be set to you electronically.

In many cases, you can self-order the labs and then send the receipts for reimbursement to your insurance. (Please check with your insurance to ensure that they will accept this and on the proper procedures.)

Thyroid Tests 101Top 10 Thyroid Tests

There are many blood tests that can be done to assess thyroid function, and I have found the following tests to be the most useful: TSH test, free T3, free T4, thyroid antibodies and a thyroid ultrasound.

The Thyroid Screening Test

TSH (Thyroid Stimulating Hormone) – This is a pituitary hormone that responds to low/high amounts of circulating thyroid hormone.

In advanced cases of Hashimoto’s and primary hypothyroidism, this lab test will be elevated (read the post about interpreting your TSH test). In the case of Graves’ disease and hyperthyroidism, the TSH will be low. People with Hashimoto’s and central hypothyroidism may have a normal reading on this test.

The thyroid stimulating hormone, or TSH test, is used as a screening test for thyroid disease, as well as a test for monitoring the correct dose of medication.

Thyroid Hormone Level Tests

Free T3 and Free T4 – These tests measure the levels of active thyroid hormone circulating in the body. When these levels are low, but your TSH tests in the normal range, this may lead your physician to suspect a rare type of hypothyroidism known as central hypothyroidism.

Thyroid Antibodies

There are various types of antibodies against the thyroid gland that can be detected in thyroid disease. The thyroid antibodies indicate that the thyroid gland has been recognized as a foreign invader by the immune system and that the thyroid gland is under attack. These antibodies can be detected for decades before changes in the other blood tests are seen.

Most Common Hashimoto’s Antibodies

Thyroid peroxidase antibodies (TPO antibodies) and thyroglobulin antibodies (TG antibodies). Most people with Hashimoto’s will have an elevation of one or both of these antibodies. TPO antibodies are the most common and have been reported in 5-38% of the population, depending on the study! Thyroid antibodies are often elevated for decades before a change in TSH is seen in Hashimoto’s.

Thyroid antibodies can be used for diagnostic purposes and monitored to track remission.

*People with Graves’ disease and thyroid cancer may also have an elevation in thyroid antibodies including TPO and TG.

You can order the entire discounted panel (TSH, free T3, free T4, TPO antibodies, TG antibodies here.)

Most Common Graves’ Antibodies

The most common antibodies found in Graves’ disease are TSH receptor antibodies, including thyroid-stimulating immunoglobulin (TSI) — this marker is elevated in >90% of people with Graves’ disease. TSH receptor binding antibody (TRAb), also known as TSH-binding inhibiting Immunoglobulin or TBII, is elevated in >50% of people with Graves’ disease. Both labs can be used for diagnostic purposes and monitored to track remission.

You can self-order both Graves’ antibody tests using the link below:
https://www.ultalabtests.com/thyroidpharmacist/Item/Item/TSI-and-TBII-Panel

The Thyroid Ultrasound

Some individuals may have thyroid disease but may not have detectable alterations in their blood work. A thyroid ultrasound will help you and your physician determine whether you have changes consistent with Hashimoto’s (such as a rubbery thyroid, shrunken thyroid, enlarged thyroid, or if abnormal growths in the thyroid are present).

Some growths may indicate an autoimmune process, others may indicate benign nodules, and others may signal cancerous nodules. I recommend at least one ultrasound for every person, especially women of childbearing age.

Thyroid Ultrasound

The Reverse T3 Test

The reverse T3 (rT3) test measures how much of the free active T3 is able to bind at thyroid receptors. RT3 is produced in stressful situations and binds to thyroid receptors but turns them off instead of activating them.

When assessing your rT3 results, it is important to watch for trends of your levels going up. This usually indicates your body is reacting to a stressful situation. Your body produces rT3 to give it a break and to prevent you from becoming hyperthyroid. This is an evolutionary adaptation to slow your metabolism in times of famine (for more information on this, take a look at my Safety Theory). High rT3 due to stress has a snowball effect on hypothyroid symptoms. The adaptation by the body producing rT3 is not useful in our high-demand society when we must work and take care of our children, spouse, parents, etc.

This test is sometimes used to identify cases of poor T4 to T3 conversion, or thyroid symptoms that are due to adrenal stress, instead of thyroid malfunction or autoimmunity. However, in most cases, this test doesn’t change my recommendations, so I consider this an optional test.

The free T4 & free T3 test is more useful for me to determine if a person is properly converting thyroid hormones. In cases where a lot of reverse T3 is produced, adding a thyroid medication that contains T3 ensures that the right hormone is getting to the right receptors.

I prefer the adrenal saliva test to determine the proper treatment for adrenal stress. An adrenal saliva test gives us the advantage of knowing how to address the reason one is producing too much reverse T3.

That said, many integrative doctors love the reverse T3 test, and it may be a useful test to monitor your improvement.

Your Symptoms

Last but not least, your symptoms should serve as the important thyroid test. Be sure to listen to your body — only you know it’s subtle messages!

Do you have any symptoms of hypothyroidism, such as: Tangled hair, hair loss, eyebrow thinning/loss, puffy face, brain fog, sadness/apathy, fatigue, cold intolerance, weight gain, joint pain, heavy periods?

Or symptoms of hyperthyroidism, such as: Irritability, agitation, mood swings, restlessness, palpitations, heat intolerance, rapid heart rate, scant periods, weight loss, insomnia, excess sweating?

 

Interpreting Your Labs

So once you have your labs, what do you do with them? What do they mean?

I frequently get messages from readers asking me to comment on their thyroid labs. Of course, I can’t provide medical advice through the internet without doing a personalized comprehensive case review (this is for your own safety as well as due to professional liability laws), so I wanted to write this little guide for you all to empower you to understand your own labs.

Please note, this evaluation is based on optimal functional medicine ranges and my clinical experience and may not be recognized by doctors who are not familiar with functional medicine.

The Reference Ranges

When I look at my client’s labs, I’m focusing on optimal reference ranges! Here’s a handy reference chart I used from the Institute of Functional Medicine.

Test Name Standard Reference Range Optimal Reference Range
TSH 0.4-5.5 IU/L 0.5-2 IU/L, 0.5-2.5 IU/L in elderly
Free T4 9-23 pmol/L 15-23 pmol/L
Free T3 3-7 pmol/L 5-7 pmol/L
Reverse T3 11-21 ng/dl 11-18 ng/dl
TPO Antibodies <35 IU/m <2 IU/m
TG Antibodies <35 IU/m <2 IU/m

What Do Highs and Lows Mean?

If you’re new to thyroid lab testing, it may seem counterintuitive, but an elevated TSH means that you do not have enough thyroid hormone on board and that you are hypothyroid. This is because the TSH is a pituitary-signaling hormone that senses low thyroid levels and is released in an effort to get the body to make more thyroid hormone.

If you’ve been a thyroid patient for a while, you’re probably thinking to yourself, “Well, of course, doesn’t everyone know that?” and I have to warn you… I’ve unfortunately seen physicians who mistakenly thought that a low TSH meant underactive thyroid and a high TSH meant an overactive thyroid, putting their patients in really dangerous situations by over or under medicating them!

So that we are all of the same page, the handy chart below explains what the thyroid lab numbers mean.

Normal Thyroid Labs

  • Lab Results:
    TSH – Normal / Free T3 – Normal / Free T4 – Normal / TPO/TG Antibodies – Negative
    Meaning: Normal Thyroid Unless Symptomatic – This is an indication that the person is euthyroid (has thyroid function within the normal level), with a low risk of Hashimoto’s/Graves’. I recommend double checking the reference ranges for optimal levels (see below), testing reverse T3, and doing a thyroid ultrasound if you still have thyroid symptoms. Adrenal saliva testing is the next step if all thyroid labs come back normal.
  • Lab Results:
    TSH – Normal / Free T3 – Low / Free T4 – Low / TPO/TG Antibodies – Positive or Negative
    Meaning: Central hypothyroidism – For some reason, the thyroid and the pituitary are not communicating. Although there are low levels of thyroid hormone around, the pituitary is not sending out a message to make more. This can be caused by the use of steroids, pituitary or adrenal issues. Autoimmune thyroid disease may be present.
  • Lab Results:
    TSH – Normal / Free T3 – Normal / Free T4 – Normal / TPO/TG Antibodies – Positive
    Meaning: Euthyroid Hashimoto’s – This means your thyroid is still making enough thyroid hormone but is under attack. This is considered Stage 2 of Hashimoto’s.
  • Lab Results:
    TSH – Elevated / Free T3 – Normal / Free T4 – Normal / TPO/TG Antibodies – Positive or Negative
    Meaning: Subclinical hypothyroidism – This means your thyroid is losing its ability to make enough thyroid hormone. This is considered Stage 2 of Hashimoto’s, especially if the antibodies are positive, although some people have seronegative Hashimoto’s — when their thyroid is under attack, but they don’t test positive for antibodies. A thyroid ultrasound can be helpful for diagnosing Hashimoto’s at this point.
  • Lab Results:
    TSH – Elevated / Free T3 – Low / Free T4 – Low / TPO/TG Antibodies – Positive or Negative
    Meaning: Hypothyroidism – This means your thyroid has lost its ability to make enough thyroid hormone. This is considered Stage 3 of Hashimoto’s, especially if the antibodies are positive, although some people have seronegative Hashimoto’s — when their thyroid is under attack, but they don’t test positive for antibodies. A thyroid ultrasound can be helpful for diagnosing Hashimoto’s at this point.
  • Lab Results:
    TSH – Low / Free T3 – Normal / Free T4 – Normal / TPO/TG Antibodies – Positive or Negative
    Meaning: Subclinical hyperthyroidism – This means your pituitary is telling the thyroid to make less thyroid hormone. The TSH may be low in the early stages of Graves’ disease, due to overmedication and in pregnancy. I recommend testing for TSH receptor antibodies if Graves’ disease is suspected.
  • Lab Results:
    TSH – Low / Free T3 – High / Free T4 – High / TPO/TG Antibodies – Positive or Negative
    Meaning: Hyperthyroidism – This means your pituitary is telling the thyroid to make less thyroid hormone because it has detected excess levels of thyroid hormone. This pattern usually indicates Graves’ disease or overmedication. I recommend testing for TSH receptor antibodies if Graves’ disease is suspected.

Your Personal Best Thyroid Numbers…

Your optimal thyroid numbers are going to be different from your mother’s optimal thyroid numbers, which are going to be different from your neighbor’s optimal thyroid numbers, so it’s important for you to track your thyroid symptoms while tracking your numbers to determine your “personal best.”

Understanding Thyroid Labs for Diagnostic Purposes

Most doctors will only run the TSH test so you will often need to ask for these additional tests. Before I go into the details as to why the TSH test doesn’t tell us the whole story, I’d like to talk about how to interpret it correctly.

In recent years, The National Academy of Clinical Biochemists indicated that 95% of individuals without thyroid disease have TSH concentrations below 2.5 μIU/L, and a new normal reference range was defined by the American College of Clinical Endocrinologists to be between 0.3- 3.0 μIU/ml. (2)

However, most labs have not adjusted that range in the reports they provide to physicians and have kept ranges as lax as 0.2-8.0 μIU/ml. Most physicians only look for values outside of the “normal” reference range provided by the labs and may not be familiar with the new guidelines. Thus, many physicians may miss the patients who are showing an elevated TSH. This is one reason why patients should always ask their physicians for a copy of any lab results.

Functional medicine practitioners have further defined that normal reference ranges should be between 1-2 μIU/ml for a healthy person not taking thyroid medications. Anecdotally, most patients feel best with a TSH between 0.5-2μIU/ml.

I have a copy of lab results from 2008, before I was diagnosed with Hashimoto’s and still searching for a reason behind my exhaustion. On these lab results, my TSH is at a 4.5μIU/ml and has a note written from the doctor: “Your thyroid function is normal, no need to do anything.” Perhaps a TSH of 4.5μIU/ml would have been normal for a 95-year-old woman, but I was 25 and sleeping 12+ hours a night to feel rested! Of course, I didn’t think to question the doctor — and most people don’t.

When I was in Poland to find distributors for the Polish version of my book, I happened to visit one of my relatives who was wearing a heavy winter coat on a warm spring day. In speaking with her, I was able to tell that she was experiencing a great number of thyroid symptoms, and she confided that her doctor had said her thyroid was normal. I looked at her labs, and sure enough, her TSH was around a 5μIU/ml, and she was never tested for antibodies and never offered a thyroid ultrasound.

I have found that I, as well as many other thyroid patients, feel best when my TSH is between 0.5μIU/ml and 2μIU/ml. Some integrative professionals will go as far as to say that people should have a TSH of right around 1μIU/ml, or below 1μIU/ml, to feel their best.

In addition to incorrect interpretations of TSH by most conventional doctors, the TSH test is not the best test to diagnose Hashimoto’s since, in the early stages, the TSH may fluctuate or remain within the normal limits.

Thus, conventional medicine practitioners will likely follow the standard reference range for TSH to determine if a person has hypothyroidism — in some cases, they may even follow a more lax range if the lab they are using hasn’t updated their levels or if the practitioner is old school. This leads to the patient being told that their thyroid is normal, when in fact, they have a thyroid condition.

Rather than digging into deeper testing in the obvious presence of thyroid symptoms, most conventional practitioners will stop further thyroid testing when they determine the TSH is “normal.”

This is why even if you’ve been told your thyroid is normal, and even if your TSH is between 0.5-2, you need to test for free T4, free T3, and especially thyroid antibodies (TPO antibodies and TG antibodies) to truly determine if you have a thyroid condition.

Why?

Because thyroid antibodies are going to be the first indication of a thyroid problem in many cases. They can be elevated for 5, 10, sometimes even 15 years before a change in TSH is detected.

And thyroid antibodies mean that there is an active destruction going on against your thyroid. This destruction often comes with a lot of symptoms that may cause/be misdiagnosed as depression, panic attacks, anxiety, miscarriage/infertility, carpal tunnel, hair loss, weight gain, fatigue/laziness, and, of course, the most disempowering diagnosis of them all… hypochondria.

Hypochondria is a diagnosis I take great offense to because it ignores the patient’s intuition that there is something wrong and often leads to shame, disempowerment, helplessness and destroys the trust we have in the healthcare model and of ever getting well.

Elevated thyroid antibodies in the presence of a “normal TSH” mean that it’s only a matter of time that your thyroid becomes destroyed to the point it can no longer produce sufficient amount of hormone. The good news is that when you have elevated antibodies and a normal TSH, you can not just reverse all of your symptoms, but you can also prevent damage to your thyroid gland.

I found out I had thyroid antibodies a year before my thyroid function deteriorated to the point where even my doctor thought I would benefit from medications. The doctor that ran the test told me not to worry about them and that there was nothing I could do anyway. I am often saddened that I trusted another person with my health and didn’t do additional research on my own. By the time I tested for TPO antibodies — they were in the 2000 IU/m range — I had developed new onset panic attacks and social anxiety. As a 25-year-old newlywed who had just moved to a new city, I was crippled by my health. Instead of focusing on being a newlywed, making wedding albums, and meeting new friends, I felt like I was falling apart. This is why I’m so passionate about advocating for you to get the proper tests and for you to understand your tests!

Thyroid antibodies may be elevated for many years before a change in TSH is seen, and finding antibodies early can often prevent damage to the thyroid and can help with preventing the need for long-term medications.

Additionally, the thyroid gland may not be correctly communicating with the pituitary — free T3 and free T4 tests may be low, while the TSH is within normal limits in some types of hypothyroidism, known as central hypothyroidism.

For those that have a family history of thyroid disorders or feel that they fit some of the symptoms of Hashimoto’s but had a normal TSH and antibody test, a thyroid ultrasound may also be helpful.

I recommend getting a full thyroid panel to get your power back. Don’t let a medical professional stand in the way of getting answers to your health challenges and solutions!

Understanding Thyroid Labs for Medication Adjustments

Thyroid labs, especially TSH, free T3, and free T4 are going to be critical for determining if you need to start, increase, or reduce the dose of your thyroid hormone medications, as well as if you’re on the right thyroid medications.

Some physicians who prescribe thyroid medications will not prescribe a medication unless the TSH is above 10μIU/ml and will be satisfied when a person who is taking thyroid meds has a TSH under 10μIU/ml. I think this is the reason why many people continue to have fatigue, cold-intolerance, difficulty with weight loss and hair loss — despite taking thyroid medications.

When the TSH is between 2.5μIU/ml and 10μIU/ml and/or T3 and T4 is within normal limits, this is known as subclinical hypothyroidism. This means that your thyroid is still able to make enough thyroid hormone, but not without sacrifice. At this point, our thyroid is working overtime, and this often leaves us with thyroid symptoms like fatigue, hair loss, and cold intolerance.

The thyroid is constantly getting a signal to make more and more hormone, and your body is likely running out of nutrients (like selenium) to make more hormone. This results in additional inflammation to the thyroid, attracting more antibodies and fueling the autoimmune process. As many as 5% of people with subclinical hypothyroidism will progress to overt hypothyroidism each year.

Starting thyroid medication in subclinical hypothyroidism is considered controversial by endocrine groups. Exceptions are made for women who are contemplating pregnancy and for those who have overt hypothyroid symptoms. Guidelines clearly state that in order to avoid pregnancy complications and impaired development of offspring, women with subclinical hypothyroidism need to be treated with thyroid hormones. (2)

At this stage, many patients may also opt to “wait and see” and may forgo thyroid medications in an effort to “do it naturally.”  I know that I was one of those people, and I waited 6 months to get on medications after my diagnosis, but knowing what I know now, I am in favor of starting medications for subclinical hypothyroidism.

Why?

Korzeniowska and Colleagues at the Medical University of Gdansk found that treating children with subclinical hypothyroidism with thyroid hormones resulted in a decrease of inflammation. This means that the medications gave their thyroids a rest and resulted in a slowing down of the autoimmune attack, manifested by lower levels of thyroid antibodies. (1)

Additionally, most patients feel so much better when they start on thyroid hormones when they have subclinical hypothyroidism.

Personally, when I was first diagnosed with subclinical hypothyroidism, I didn’t want to take medications because I felt like it would be giving up and that I should figure things out naturally. At that point, I started weekly acupuncture, Brazil nuts and was using all kinds of magic hair potions to try to keep my hair loss at bay (I was still a young butterfly then).

I wanted to believe that these interventions were keeping me from getting worse until my husband and I took a red-eye flight from Los Angeles to visit friends on the East Coast in the winter. The lack of sleep combined with the cold weather put me in a hypothyroid flare.

I spent the entire weekend shivering, tearful, and anxious and was very embarrassed about how much I inconvenienced our friends.

After I flew back to California, I spent a few days getting nourishment from the sun and made an appointment to start medications. I felt much better when I did, and thus I’m no longer a proponent of being a martyr for a senseless cause. Part of loving yourself is knowing when you need help.

If I could do it over, I would have, of course, gone gluten, dairy, and soy free for three months as soon as I found out I had Hashimoto’s AND started medications. If a three month trial of diet didn’t result in significant improvement, I would have started digging for my root cause.

After all, when my TSH was at 4.5μIU/ml, I was sleeping for 12+ hours, and at 3 μIU/ml, my hair begins to tangle. I didn’t realize how hypothyroid I was until I was appropriately treated. A little change in the dosage of thyroid medication can make a huge difference.

Please take a look at my article on TSH for a letter you can take to your physician if he/she is not familiar with the current reference range. Personally, I feel best with a TSH a bit under 1μIU/ml, but you may need some trial and error to find your personal best TSH.

T4 to T3 Conversion

There are four main thyroid hormones that have been identified: T1, T2, T3 and T4.

T4 (thyroxine) and T3 (triiodothyronine) are the two main thyroid hormones. T4 is known as prohormone and is 300% less biologically active than T3. T3 is the main biologically active thyroid hormone and gives us beautiful hair, energy, and runs our metabolism.

You may have put together that most of the commonly prescribed thyroid medications like Synthroid and Levothyroxine only contain T4 (thyroxine), and thus they need to be converted to T3 in the body.

On paper, the T4 to T3 conversion happens just fine, but in the real world, in real human bodies, we may not always convert T4 to T3. Proper lab testing can reveal this.

There are two ways to test the thyroid hormones. Total hormone levels measure all of the thyroid hormones in the body, but they may not paint an accurate picture of the situation. “Free” hormone levels measure the hormone that is available to do its job in the body. Thus, tests for free T4 and free T3 are recommended.

Some clinicians may only test for T4, but T3 is also important to test, as some individuals may not be converting the T4 to the active T3 properly. Thus, people may have a normal T4, but a low T3 level.

Reverse T3 (rT3) is also a test that can be done to see how much of the free active T3 is able to bind to thyroid receptors. RT3 is produced in stressful situations and binds to thyroid receptors, as well, but turns them off instead of activating them.

How Do You Know If You Are Converting Correctly?

 

Take a look at your free T3 and free T4 levels. Both should be in the optimal range. If the T4 is optimal, but the T3 is out of the optimal range, you know that your body is not making enough T3 hormone from the T4. You may want to read about the different hormone preparations in my article Which Thyroid Medications Is Best?

And I’d love to give you my 100-page eBook Optimizing Thyroid Medications (a $19.99 value!) for free, when you sign up HERE.

This eBook does a deep dive all about the various thyroid medication options, how to take them properly, and how to work with your doctor to get the right medication and the right dose!

How Often to Test?

While you’re trying to figure out the correct dose, retesting TSH, free T3, and free T4 every 4-6 weeks is a good timeframe for retesting. Once you establish a dose that’s working for you — and as long as your symptoms don’t change (look out for anxiety and palpitations as a potential sign of an overdose, and fatigue and pain as a potential sign of an underdose) — you can test every six months.

Understanding Thyroid Labs for Monitoring Remission

Thyroid antibodies can be used as a marker to monitor disease progression and remission. I recommend a lot of strategies to make the condition less aggressive and to put it into remission in other articles on my websites as well as in my books Hashimoto’s the Root Cause and Hashimoto’s Protocol.

With respect to thyroid antibodies (TPO antibodies and TG antibodies), I recommend monitoring them every 90 days to see if the changes you’re making in your lifestyle are helping you. A reduction in these antibodies, especially when accompanied by a reduction in symptoms, is a good indication that your condition is improving and that you are on the right path with your interventions.

What the thyroid antibody numbers mean…

  • Thyroid antibodies above 500 IU/mL are considered aggressive
  • Antibodies under 100 IU/mL indicate remission
  • Antibodies under 35 IU/mL mean you no longer test for Hashimoto’s according to conventional standards
  • Antibodies under 2 IU/mL are optimal

The Bottom Line…. Which Tests Should You Get?

I tried to write the most comprehensive and helpful article on interpreting thyroid labs based on the questions I’ve received from my readers and clients in the last few years. This has been a long time in the making 🙂 Can you let me know how I did? Was this article helpful? Did you have an “Aha” moment? Do you have additional questions for me about labs?

You can also download a free Thyroid Diet Guide, 10 Thyroid friendly recipes, and the Nutrient Depletions and Digestion chapter for free by going to www.thyroidpharmacist.com/gift. You will also receive occasional updates about new research, resources, giveaways and helpful information.

References

  1. Katarzyna K, Jarosz C, Agnieszka S et al. L-thyroxine Stabilizes Autoimmune Inflammatory Process in Euthyroid Nongoitrous Children with Hashimoto’s Thyroiditis and Type 1 Diabetes Mellitus. Journal of Clinical Research in Pediatric Endocrinology. 2013;5(4):240-244. doi:10.4274/jcrpe.1136.

Source:thyroidpharmacist.com

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