Free Triiodothyronine T3


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T3 or triiodothyronine is the active form of the thyroid hormone. T3 acts as a metabolic throttle for fueling all of the daily cellular functions. Free T3 is the unbound portion of T3 that is biologically active.


  • This test measures the amount of T3 not bound by proteins and available to the tissues, or free T3.
  • Many doctors believe that evaluating the levels of free T3 is the best indicator of thyroid function
  • Needed to determine the level of active thyroid hormone primarily responsible for regulating metabolism to fuel all cellular functions
  • Reference Interval: 2.0−4.4 pg/ml (>19 yr old)
  • Methodology: Electrochemiluminescence Immunoassay (ECLIA)

Free T3 Triiodothyronine Test - What It Is and Why You Need One


You already know that the thyroid gland is responsible for your body's metabolism and energy production. This is entirely true and it's possible because of the main thyroid hormones - T3 and T4. Free T3 triiodothyronine is particularly important in this case.

The T3 hormone instructs various organs and tissues in your body on how to metabolize enzymes and produce energy for general use. When you have too little or too much T3, you will experience certain symptoms.

Keep reading to find out more about T3 and why you should test for this hormone in the near future.

What is Free T3 Triiodothyronine?

As mentioned earlier, T3 is a hormone produced by your thyroid gland. This hormone is mostly bound to protein in your body. However, a small fraction of T3 is unbound and it's also known as free triiodothyronine.

Measuring the levels of free T3 triiodothyronine is done using a simple blood test. This is useful in diagnosing certain thyroid problems or other medical conditions in your body. If your free T3 levels are out of balance, more tests might be needed to find out the nature of your thyroid issue.

T3 and The Thyroid Gland

It's important to note that the free T3 hormone is just a part of a larger picture. Your pituitary gland releases a hormone called thyroid-stimulating hormone (TSH). This hormone tells your thyroid to produce healthy levels of T3 and T4.

These thyroid hormones instruct other glands and organs in your body to perform their duties. T3 and T4 are responsible for various metabolic processes, energy production, cognitive functions, and more. If you feel tired or lacking energy on a regular basis, chances are that your thyroid hormones are the culprit.

T3 and T4 are also responsible for regulating body temperature. If you regularly feel cold, even during warm seasons, it might be because your T3 levels are out of balance. Thyroid hormones are also in charge of regulating your heart rate, liver, and kidney function, and more.

As you can see, it's important to check your T3 levels regularly because this and other thyroid hormones dictate most of your body's activity and metabolic processes. Luckily, abnormal T3 hormones also show some symptoms.

Symptoms of Abnormal T3 Levels

One of the main symptoms caused by a thyroid problem is excessive tiredness, even after a good night's sleep. However, this symptom is also caused by other health issues. That's why you need to specifically test T3 levels to see if this is the real cause of your chronic fatigue.

Other symptoms of abnormal T3 levels include:

  • Constipation
  • Anxiety and depression
  • Weight loss
  • Brittle hair and nails
  • Dry skin
  • Increased heart rate
  • Sleeping problems

These are just a few of the symptoms experienced by people who have thyroid problems. However, they are common with other diseases and that's why you need to do a T3 test to see if your thyroid gland is really the culprit.

Some of these symptoms also last for days, weeks, or even months. Most people ignore them, but this is a bad idea. Thyroid problems can only get worse, so make sure that you test your thyroid hormones frequently, especially if you experience persistent symptoms like the ones mentioned above.

What Are the Normal T3 Levels?

Normal T3 levels range between 100 and 200 ng/dL. Anything higher or lower than that signifies a potential thyroid problem. However, keep in mind that T3 is only one of the main thyroid hormones. It's recommended to also check your T4 and TSH to get the full picture when it comes to your thyroid health.

What Do Abnormal T3 Results Mean?

Having elevated levels of T3 is usually caused by hyperthyroidism. This is a condition in which the thyroid gland produces excessive T3 and T4 hormones. This could be caused by a poorly functioning pituitary gland, or it might be linked to other health issues.

High T3 levels can also be caused by Graves' disease or by a toxic nodular goiter. In very rare cases, having too much protein in the blood can also make T3 levels increase abnormally. Keep in mind that pregnant women usually have high T3 levels and they are not caused by disease.

Liver problems might cause high T3 levels too. Some people have healthy thyroid glands, but the liver disease is making the thyroid produce excess T3. That's why certain doctors also order additional liver tests to see what's wrong with this organ.

At the other end of the spectrum are very low levels of T3 which are usually caused by diseases that require hospitalization. Low T3 levels are also associated with hypothyroidism. This means that your thyroid gland is not producing enough hormones for various reasons.

What Is a Thyroid Panel Test?

As you can see, individual thyroid tests such as free T3 or T4 are useful enough to diagnose various conditions. However, most doctors would also recommend other thyroid-related tests such as T4, TSH, and others. These help you get the full picture when it comes to the health of your thyroid gland.

Luckily, you can also do that yourself using a thyroid panel. This is a combination of tests in one place that help you cover all the aspects when it comes to your thyroid gland. Such panels are sometimes less expensive than the individual tests put together, so you might also save some money.

Order Your T3 Test Today!

Whether you go for a simple T3 triiodothyronine test or a complex thyroid panel test, this is the right thing to do. You will find out more about the health of your thyroid and act early if your hormones are out of order.





T3 Test: Purpose, Procedure, and Risks

Essentials About Thyroid Hormones and Reverse T3




  1. Go to the "Find a Location" page to find the closest lab location. No need to make an appointment since walk-ins are welcomed. Once you have identified your closest location, go to step 2.

  2. Go to "Choose a Test" and add your selection (s) in the shopping cart. If you prefer to save money on bundled tests, we have created "Lab Test Panels" that can help you decide what to order.

  3. If you have a discount coupon code, add it to your cart.

  4. A $8 lab processing fee will be added to your total.

  5. Pay using a credit card.

  6. You will receive an order confirmation and instructions email on how to download your lab request.

  7. Print lab request form that you downloaded.

  8. Take that form to the closest location. Get your blood drawn.

  9. You will receive an email when the results are ready for you to download.

    Note: You cannot place an order under someone else's profile. The profile person's name will appear on the lab order form.


    If you have further questions, please email [email protected].

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