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Understanding Your Thyroid Test Results

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Science Based

Written by  Amy Myers, MD

Your thyroid is a complex organ that wears many hats. Because of this, I often get asked a lot of questions. Some of the most frequent questions I get is, “How do I interpret my thyroid test results, and which tests are most important?” These are important questions to ask, and let me tell you, there is a lot of misinformation out there. Both the internet and conventional medicine world have a lot of misinformation surrounding thyroid tests, thyroid test results, and thyroid medication. That’s why I discuss them in-depth in my book, “ The Thyroid Connection .”

I’ll explain the different types of thyroid tests, as well as how to interpret your thyroid test results. Also, I’ll go over why your doctor should carefully review your thyroid test results. This is important, because what may be “normal” is not necessarily optimal. There are optimal reference ranges for thyroid test results you can aim for. This can help you and your doctor ensure you enjoy the benefits of optimal thyroid levels.

Types of Thyroid Hormone Tests & Optimal Thyroid Levels

Many doctors who suspect a thyroid disorder start by checking Thyroid Stimulating Hormone (TSH) test levels. TSH tests usually reveal whether someone is dealing with hyperthyroidism vs hypothyroidism.  TSH acts like an “early warning sign” and will usually give a clue that something could be heading in the wrong direction. 

If they’re lucky, a doctor might test a person’s Free T4 levels. Free T4 shows if there’s a shortage of the storage form of thyroid hormones. While these thyroid test results do a great job to uncover the nature of a patient’s disease, they only tell you a small part of the story.

Other thyroid tests include T3 tests, Free T3, and Reverse T3. There are also thyroid antibody tests. To get a complete picture of a patient’s thyroid health and medical needs, I recommend working with a doctor who orders all six blood tests listed below.

Thyroid Stimulating Hormone (TSH)

The hypothalamus is the control center of your brain. It is responsible for managing many body functions. For example, hunger, thirst, sleep, hormones, and body temperature, among other processes. The hypothalamus also continuously monitors the level of thyroid hormones present in your bloodstream. 1 If it determines that energy levels are low, it sends out TRH, or Thyroid Releasing Hormone, to your pituitary gland.

Your pituitary gland receives the TRH and responds by releasing TSH, or Thyroid Stimulating Hormone. TSH goes directly to your thyroid to produce more thyroxine, or T4. Your TSH level is an indication of what your pituitary gland is doing. We know this based on your hypothalamus’ feedback loop. The problem is that it’s not actually an indicator on how your thyroid is actually functioning. As a result, there is a misunderstanding of thyroid test results. This often leads to counterintuitive patient advice.

TSH Thyroid Test Results

• If your TSH test level is high in your thyroid test results, this can be a sign that you are under-producing thyroid hormones and you are hypothyroid.
• If your TSH test level is low in your thyroid test results, this can be a sign that you are over-producing thyroid hormones and are hyperthyroid. Or, it could also mean you are on too much supplemental thyroid hormone. Supplemental T3, or natural desiccated thyroid hormone with T3, can artificially suppress your TSH levels. So, in the absence of symptoms, it could be perfectly fine if the level appears low.

Normal vs Optimal Thyroid Levels

If your thyroid test results show “normal” TSH test levels, you may not have a thyroid dysfunction. By “normal”, I mean it falls within the normal reference range used by most conventional doctors. However, as I write in my book , “normal” and “optimal” levels mean very different things. If you still have symptoms yet fall within the “normal” range for thyroid test results, you may still have thyroid dysfunction. One example of this includes subclinical hypothyroidism. 2

What is T4, or the Storage Form of Thyroid Hormone?

Once TSH signals your thyroid to ramp up hormone production, it produces several different types of thyroid hormone. For example, your thyroid releases T1, T2, T3, and T4. It also releases calcitonin, which helps regulate calcium. The primary output of your thyroid is T4, which is a storage form of the hormone. It circulates throughout the bloodstream and stays in the tissues. That way, it’s available when needed. I like to measure Free T4 (FT4) since it is unbound and able to act in the body.

Free T4 Thyroid Test Result

• If your Free T4 level is high in your thyroid test results, it can mean an overactive thyroid or hyperthyroidism. 
• If your Free T4 is low in your thyroid test results, it can mean an under-active thyroid or central hypothyroidism.

What is Free T3, or “the Gas”?

When each local area of your body determines that it needs more power, it converts storage T4 and Free T3. While T4 is the storage form of thyroid hormone, T3 is the active form of the hormone. These hormones attach to receptors inside of your cells to power your metabolic processes. This is why I like to think of them as the gas. 3

Free T3 Thyroid Test Result

• If your Free T3 level is high in your thyroid test results, it indicates that your thyroid is overactive or hyperthyroidism.
• If your Free T3 is low in your thyroid test results, you may not be converting T4 to Free T3 very well. You could have hypothyroid symptoms, even if your TSH level and Free T4 level are within the “normal” range in thyroid test results. This is one of the most common causes of low thyroid or hypothyroidism that I saw in my clinic.

What is Reverse T3, or “the Brakes”?

Your body also uses some of the T4 to create Reverse T3 (RT3). Reverse T3 is another inactive form of thyroid hormone. This one can attach to the receptors for Free T3 to slow down your metabolic processes. For that reason, I call RT3 the brakes. 4

Reverse T3 Thyroid Test Result

• If RT3 is high – you are likely converting too much T4 to RT3 and not enough to FT3. This can cause hypothyroid symptoms, even if your TSH and T4 levels are optimal. 
• Also, I look at something called an RT3:FT3 ratio. I like that to be less than a 10:1 ratio.

What are Thyroid Antibodies?

The vast majority of thyroid conditions are autoimmune. Autoimmune conditions happen when your immune system attacks itself. In this case, your immune system attacks your thyroid. The hypothyroid form of autoimmune thyroid disorder is Hashimoto’s. On the flip side, the hyperthyroid form (which is what I had) is Graves’ disease. It’s incredibly important to know if your thyroid condition is autoimmune . After all, once you develop one autoimmune disease, you’re more likely to develop another.

There’s another reason this is important. As I explain in both of my books, The Thyroid Connection , and The Autoimmune Solution , addressing the root cause can help reverse autoimmune disease. Some of the biggest causes include leaky gut , diet, toxins , infections, and stress .

There are two main types of thyroid antibodies. The first type is thyroid peroxidase antibodies (TPOAb). These attack an enzyme used to synthesize thyroid hormones. TPOAb are commonly elevated in both Hashimoto’s and Graves’ disease patients. Thyroglobulin Antibodies (TgAb), attack thyroglobulin, which your thyroid uses to produce its hormones. These thyroid antibodies are typically elevated in Hashimoto’s patients.

Thyroid Antibodies Test Result

• If your antibodies are high, your immune system is attacking your thyroid. This could mean one of two outcomes. Either you have autoimmune thyroid disease, or you are on the Autoimmune Spectrum® .

What Thyroid Tests Should Your Doctor Order?

Most conventional medicine doctors only check your Thyroid Stimulating Hormone (TSH) levels and Free T4 levels to see if you are low on the storage form of thyroid hormones. However, as we’ve just covered, optimal thyroid function involves many factors. Those two levels of thyroid test results alone don’t tell the whole story. I recommend ordering the following tests to get a complete picture of a patient’s thyroid problems and health.

• Free T4 
• Free T3 
• Reverse T3 
• Thyroid Peroxidase Antibodies (TPOAb)
• Thyroglobulin Antibodies (TgAb)

The Optimal Thyroid Levels

Even if your doctor does order a complete thyroid function test panel, they’re usually relying on “normal” thyroid test results reference ranges that are too broad and often inaccurate. When lab reference ranges for a healthy thyroid were created, it was later discovered that people who already had thyroid dysfunction were included in those ranges! 

Because of this, in 2003, the American Association of Clinical Endocrinologists recommended that the lab reference ranges for thyroid test results become more narrow. Yet still today, most doctors and laboratories haven’t updated their practices for optimal thyroid levels.

In my clinic, I found that the ranges below are where my patients (and myself) thrived, not just lived! I listened to my patients and took how they were feeling into account as well. 5

  I believe the most optimal thyroid levels are:

• TSH levels of 1-2 UIU/ML or lower (Armour or compounded T3 can artificially suppress TSH)
• FT4  levels >1.1 NG/DL
• FT3 levels > 3.2 PG/ML
• RT3 levels < 10:1 ratio RT3:FT3
• TPO – TgAb levels < 4 IU/ML or negative

If Your Doctor Won’t Order a Full Thyroid Panel for You

My sincere hope is that your doctor is willing to order all of the labs listed above and then use the optimal thyroid levels reference ranges while working with you to restore your optimal thyroid levels. However, if that is not the case, I recommend using a lab company such as My Labs for Life so that you can easily order a complete thyroid panel and take your results back to your physician to have them reviewed.

The Myers Way® to Support Thyroid Health

The Myers Way® Multivitamin is tailor-made to help support optimal thyroid levels. I personally lived with thyroid issues. I’ve spent my career perfecting the art of supporting thyroid health for myself, the patients in my clinic, and, now, anyone who wants to support healthy thyroid and adrenal function. I custom-formulated this multi to be the perfect multivitamin for virtually everyone. However, I created it for those with thyroid dysfunction in mind. In fact, all of my patients with hypo- or hyperthyroidism, including Hashimoto’s and Graves’ disease, had my daily multivitamin in their treatment plans.

This specially-formulated multi is jam-packed with micronutrients in the forms your body wants and the amounts your thyroid needs. With optimal levels of thyroid-supporting minerals such as zinc, selenium, and iodine, alongside antioxidants including vitamins C and E and other free radical scavengers, no other multivitamin on the market does more to support your thyroid!

Article Sources

• Physiology of the Hypothalamic-Pituitary-Thyroid Axis . Stefano Mariotti, Paolo Beck-Peccoz. NCBI. 2016.
• High and low TSH Levels: What They Mean . Mary Shomon. Very Well Health. 2019.
• What to Know About T3 Levels . Aaron Kandola. Medical News Today. 2020.
• Overview of Reverse T3 Thyroid Hormone . Mary Shomon. Very Well Health . 2020.
• Interpreting Thyroid Levels Tests . Corey Whelan. Healthline. 2019.

The Myers Way® Multivitamin

Amy Myers,  MD

Amy Myers, MD is a two-time New York Times bestselling author and an internationally acclaimed functional medicine physician. Dr. Myers specializes in empowering those with autoimmune, thyroid, and digestive issues to reverse their conditions and take back their health. In addition, she is a wife, mother, and the successful  founder and CEO of  Amy Myers MD ® .

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What Is a Total Thyroxine (T4) Test?

What to expect when undergoing this test

Purpose of Test

Before the test, during the test, after the test, interpreting results.

The total thyroxine test is used to diagnose thyroid disorders . Thyroxine (T4) is a thyroid hormone, and the test measures how much is in your blood. Some thyroid diseases are tied to too little T4, and others are tied to too much.

Other names for this test are a total T4 test, total T4 concentration, and a thyroxine screen.

The thyroid is a gland in the front of your throat that makes hormones and regulates a variety of important functions including energy use, weight, body temperature, and mood.

T4 functions in your body in a couple of forms. One form bonds with a protein to perform certain tasks and another form doesn't, which allows it to perform different jobs. The total T4 test checks total T4 levels, which includes both forms and free T4, which is the form not bonded with a protein.

The level of total T4 is greatly dependent on the amount of binding protein in the blood, and the amount of protein is influenced by many nonthyroid conditions. So the total T4 measurement may not accurately reflect the condition of the thyroid. For this reason, the free T4 test, which measures only the active, unbound portion of T4 in the blood, is considered a much superior test, and it has largely supplanted the total T4 test in clinical medicine.

Your healthcare provider may order a total T4 test if you have symptoms that could indicate hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid), especially if you have other risk factors such as being female and over the age of 60 or you have family members with thyroid disorders .

Your healthcare provider will likely order other measurements of thyroid function at the same time as a T4 test.

These generally include tests of thyroid stimulating hormone (TSH) and triiodothyronine (T3). Tests to look at antibodies that could indicate autoimmune disease may also be done at the same time or may be done as a follow-up to abnormal thyroid-function tests .

Low levels of T4 could lead to more testing to determine whether you have an autoimmune thyroid disease called Hashimoto's thyroiditis. High levels may lead to testing for Graves' disease , thyroiditis, or goiter.  

The T4 and other thyroid tests are performed on blood samples. Taking blood samples is fairly quick, simple, and low risk.

The most common risks people face from a blood test is slight pain or mild bruising afterward, which should go away quickly.

Some people, especially those who are afraid of needles, may experience dizziness, nausea, or ringing in the ears during or immediately following a blood draw. If this happens to you, let someone at the medical center know. Most facilities are well equipped to deal with this reaction, which usually involves lying down for a while and drinking some water.

If you have a history of negative reactions, you may want to arrange for someone to drive you to and from the test facility.

Let the nurse or phlebotomist who is drawing your blood know before the test if you've had bad reactions to blood draws in the past, you have a bleeding disorder or are taking blood-thinning medications, or if your skin tears or bruises easily. They should be able to mitigate any risk these elements may create.

Blood for T4 and other thyroid tests can generally be drawn at any time of day. It doesn't require fasting (avoiding food) beforehand.

Be sure to have your insurance card and any written orders your healthcare provider may have given you.

Talk to your healthcare provider about any medications you're taking and whether they could alter your test results.

• You may need to take a break from certain medications, if your endocrinologist advises it. These include:
• Some cancer drugs
• Thyroid medications (unless you're being checked for how effective the medication is)

Other drugs may impact results as well, and so could supplements, so make sure your healthcare provider is aware of everything you're taking. Biotin, in particular, interferes with thyroid assays. Patients should stop biotin three days before a thyroid test, especially if the dosage is exceeding 5,000 mcg per day.

Birth control medications as well as pregnancy can also affect your thyroid hormone levels, so make sure your healthcare provider knows if you are or could be pregnant.

Timing and Location

The blood draw itself should just take a few minutes. If you're getting multiple tests, it could take slightly longer. If the blood is being drawn in your healthcare provider's office during an appointment, it should add very little time to the appointment length.

Going to a lab for the test can require a larger time commitment. If you have a scheduled time for your test, be sure to arrive early enough to check in and pay any copays that may be due at the time. If you're anxious about the test, you may also want to give yourself a few minutes to sit calmly and relax.

Labs are often busy, so if you're dropping in, you may want to call ahead of time or aim for a time of day (such as early in the morning) when they tend to be less crowded.

What to Wear

You should be able to stay in your own clothing for the blood draw. Your arm will need to be exposed, so sleeves that are short or can be pushed up easily are best.

In case of a dizzy spell, you may want to wear flat shoes and clothing that's not tight and constricting.

Food and Drink

Any time you're having blood drawn, you should be sure you're well hydrated. That helps your veins keep their shape, which means it's easier to find them and successfully insert the needle.

Since you don't need to fast before a T4 test, it's a good idea to have something in your stomach, which may help avoid any nausea.

If your healthcare provider is ordering other tests at the same time, however, some could require fasting. Be sure to follow all of the instructions you're given by the practitioner and/or the lab performing the test.

Cost and Health Insurance

Typically, thyroid function tests are covered by insurance when they're deemed medically necessary. If you have any questions, be sure to call your insurance company ahead of time to see what, if any, out-of-pocket expenses you could face.

Laboratory costs for a total T4 test can range from $45 to about $130. If you're not insured, you may face additional charges on top of that, especially if your healthcare provider is ordering more than one test. A full set of thyroid tests may cost more than $500.

Your healthcare provider's office, insurance company, and lab should be able to help you determine the cost before you get the tests.

Before the blood draw, the nurse or phlebotomist may ask you to confirm certain information such as your name, birth date, healthcare provider ordering the test, and what test you've been sent for. This is to help prevent errors.

You'll be asked to expose your arm, and the insertion area will be cleaned with alcohol. The person performing the draw will tie a band around your upper arm to trap blood in your veins, which makes it easier to find a good vein and insert the needle. If your veins aren't standing out well, you may be asked to pump your fist.

Throughout the Test

Once a good vein is identified, the needle will be inserted. The band will be released to get the blood flowing again, and the vial attached to the needle will fill up. Depending on how many tests are ordered, the nurse/phlebotomist may need to change vials one or more times.

After the requisite blood has been drawn, the insertion site will be bandaged.

Most of the time, you can leave right away after a blood draw. If you have any kind of negative reaction, let someone at the facility know so you can get the proper care. Usually, even with a bad reaction, people are OK after a few minutes.

You may have a little soreness and bruising around the site where the needle was inserted, which typically goes away in a short amount of time. If you have any problems or questions, be sure to contact your healthcare provider.

Managing Side Effects

If the site is sore, you may want to ice it or take over-the-counter pain medication. You shouldn't have any other lingering effects from a simple blood draw.

In adults, the typical range for free T4 is between .9 and 2.o nanograms per deciliter. Total T4 tends to vary more with age.

An abnormally high T4 level may indicate hyperthyroidism, thyroiditis, or goiter. It may lead to additional tests for Graves' disease.

An abnormally low T4 level can be a sign of hypothyroidism, a problem with your pituitary gland, malnutrition or iodine deficiency, or other illness. It may lead to further tests for Hashimoto's thyroiditis.

However, an abnormal T4 level alone doesn't usually lead to a diagnosis. Your healthcare provider will likely analyze it along with T3 and TSH levels.

Once you have the results, your healthcare provider may want you to come back in to discuss further testing or treatment options, depending on whether a diagnosis has been made. If you don't hear back about your results in a timely manner or if you don't understand what they mean, contact your healthcare provider's office. If you are diagnosed with a thyroid disorder, then it's time to look into treatment options as early treatment is key.

A Word From Verywell

Thyroid disorders are common (especially in women) and highly treatable. Many thyroid diseases are managed by taking medication and possibly making some dietary changes. While being diagnosed with a thyroid disorder can be scary, the upside is that it means you can start treating and managing the condition, which should mean feeling and functioning better.

Shahid MA, Sharma S. Physiology, Thyroid Hormone . In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing.

National Institute of Diabetes and Digestive and Kidney Diseases. Hypothyroidism (Underactive Thyroid) .

National Institute of Diabetes and Digestive and Kidney Diseases. Hyperthyroidism (Overactive Thyroid) .

Sarne D. Effects of the Environment, Chemicals and Drugs on Thyroid Function . In: Feingold KR, Anawalt B, Boyce A, et al., editors. Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc.

Henze M, Brown SJ, Hadlow NC, Walsh JP. Rationalizing Thyroid Function Testing: Which TSH Cutoffs Are Optimal for Testing Free T4? . The Journal of Clinical Endocrinology & Metabolism. 2017;102(11):4235-4241. doi: 10.1210/jc.2017-01322

Sheehan MT. Biochemical Testing of the Thyroid: TSH is the Best and, Oftentimes, Only Test Needed – A Review for Primary Care. Clinical Medicine & Research . 2016;14(2):83-92. doi: 10.3121/cmr.2016.1309

Welsh KJ, Soldin SJ. How reliable are free thyroid and total T3 hormone assays? . European Journal of Endocrinology. 2016;175(6):R255-R263. doi: 10.1530/eje-16-0193

By Adrienne Dellwo Dellwo was diagnosed with fibromyalgia in 2006 and has over 25 years of experience in health research and writing.