Reverse T3 Lab Test


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The reverse T3 test has to be done at the same time you do the free T3, and you then measure the ratio between the two by dividing the RT3 into the Free T3. The body produces the benign RT3 naturally to rid itself of excess of T4, but in some cases, such as high or low cortisol, RT3 is produced in excess which can clog cell receptors from receiving T3. FT3 is usually twenty or more times higher than RT3.

The thyroid produces two main hormones - T4 and T3. However, a small amount of reverse T3 is also produced. This is often overlooked when testing thyroid hormones and it can be a mistake. Keep reading to learn more about reverse T3 and why it is so important.

Reverse T3 - Symptoms, Causes, and Why Is It Important for Thyroid Health


As you probably know already, your thyroid gland is one of the most important organs in the body. It instructs other organs and tissues to produce hormones and exchange chemicals to keep up your metabolism and make you "work" every day.

The thyroid produces two main hormones - T4 and T3. However, a small amount of reverse T3 is also produced. This is often overlooked when testing thyroid hormones and it can be a mistake. Keep reading to learn more about reverse T3 and why it is so important.

What is Reverse T3?

Reverse T3 (rT3) is an inactive form of T3. It is produced by your body as a method to flush out excess T4. T3 should nousuallye twenty times more than reverse T3. However, in some circumstances, the body converts too much T4 into rT3 instead of free T3.

This is when a patient starts to experience thyroid problems and their associated symptoms. Since not enough T3 is produced (because it's replaced by rT3), the patient might be diagnosed with subclinical hypothyroidism. This means that the thyroid doesn't produce enough healthy hormones to make your body function correctly.

Knowing your rT3 number is important for a variety of reasons. For example, your thyroid might produce an adequate quantity of T4, but a lot of it is converted to rT3 instead of free T3. If you go to a doctor for a thyroid test, he might diagnose this condition as hypothyroidism.

The next step would be to prescribe thyroid medicines that usually increase the production of T4. This will not help you as more rT3 will be produced as a result, nstead of free T3. By testing your rT3 and establishing the reverse T3/free T3 ratio, your doctor can detect the real problem that might affect your thyroid gland.

What Is the Normal Range of  Reverse T3?

According to LabCorp, the normal range of rT3 in the body for adults should be between 9 and 24 ng/dL of blood. Anything higher than that means that your body is converting more T4 into rT3 instead of free T3 which is the active thyroid hormone.

When this happens, a patient will eventually get the classical symptoms of hypothyroidism. That's because less T3 is produced and this will have an effect on health and wellbeing. rT3 competes with free T3 for receptors in the body.

What Are the Symptoms of Having Too Much rT3?

The good thing is that your body will let you know that the thyroid hormones are not balanced out. Here are some of the most common signs of having high levels of rT3. These symptoms are relatively similar to those found in patients with diagnosed hypothyroidism.

  • Excessive fatigue, even after a good night's sleep
  • Unexplained weight gain
  • Anxiety and depression
  • Slowed-down heart rate
  • Sensitivity to cold
  • Dry skin and hair
  • Muscle aches and cramps
  • Joint pain

In many cases, you might have these symptoms for years before you finally find out that your thyroid is not functioning properly. You shouldn't ignore these symptoms and try to get an rT3 test as well as a T3 and T4 test to determine why your thyroid is not working correctly.

What Are the Causes of Excessive rT3?

Doctors and medical scientists have found ways to discover why your body is converting too much T4 into rT3 instead of T3. Some health conditions facilitate this conversion and can lead to a buildup of rT3 over time.

Here are some of the most common causes of having too much rT3 in your body.

  • Chronic conditions such as diabetes, arthritis, and fibromyalgia
  • Eating disorders such as anorexia and eating low-calorie diets
  • Autoimmune diseases such as Hashimoto's disease, lupus, and others
  • Excessive mental/emotional stress
  • Extreme training programs including heavy weightlifting and running marathons
  • Taking certain drugs such as antidepressants, beta-blockers, and others

These conditions might be the reason why your thyroid is producing too much rT3 instead of free T3. It's important to run an rT3 test and then talk to your doctor to rule out these health issues one by one. In some cases, just a personal problem such as a divorce or the loss of a loved one can spike your rT3 levels.

What Are the Treatment Options for Elevated rT3?

If indeed your thyroid is producing too much rT3 instead of free T3, you need to look at various treatment options to restore its normal function. For example, iodine is a supplement that helps with the conversion of T4 into free T3.

Another important supplement is selenium. Your thyroid requires a decent quantity of selenium to produce hormones the right way. You might want to supplement with this mineral, following your doctor's recommendations.

Zinc is another supplement that can help restore your thyroid's natural function. Supplementing with zinc on a regular basis might make your thyroid switch back to converting more T4 into T3 instead of reverse T3.

At the same time, certain compounds such as bioidentical T3 can be taken to replenish your stores of free T3 and flush out excess rT3 from your system. Once you get rid of the reverse T3, a process that could take a few months, your hypothyroidism might also cure itself naturally.

Order Your Reverse T3 Test Today!

As you can see, testing your reverse T3 is important because this often-overlooked substance might be the culprit of your constant fatigue and/or depression. Most conventional doctors don't always take rT3 into account, but now you know you shouldn't make this mistake.

At the same time, it's recommended to test your free T3 and T4 levels together with rT3 to get the whole picture. Your thyroid is a complex organ and you need to look at it from various angles to determine exactly why it's not producing hormones correctly.

Go to today and get your reverse T3 test to learn more about your thyroid and your body in general!


NOTE: If you are taking biotin, please stop it 72 hours before the blood draw since it may interfere with hormone blood tests.


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  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.

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