Issue 5: Lack of testing for Free T3 and Reverse T3 levels

Every organ and every cell requires T3 hormone for proper function. In fact, T3 is so important that all other thyroid hormones exist mainly to protect and regulate our T3 levels. Reverse T3 mimics the molecular shape of T3 but has no effect other than plugging up cells’ T3 receptors.  Healthy levels of T3 and Reverse T3 prevent thyrotoxicosis, but if RT3 dominates T3, it can lead to T3 deprivation, which leads to a very poor prognosis in acute or chronic illness.

This series of 6 blog posts tells my story and outlines the six challenges I’ve faced.

This post focuses on the importance of regularly testing “T3” and “Reverse T3” hormone levels in the blood of hypothyroid patients to ensure that therapy is achieving its ultimate goal of adequately replacing the most important thyroid hormone, T3.

At almost every turning point in my experience with Hashimoto’s thyroiditis, I have had to do my own research and take initiative to ask my doctors for tests that should have been done years earlier.

On top of my hypothyroid symptoms (during treatment as well as pre-treatment) and the fact that chronic hypothyroidism increases risk for other health issues (such as heart problems), I have struggled with systemic barriers in the health care system:

  1. Delayed diagnosis of hypothyroidism
  2. Misdiagnosis of thyroid-related depression
  3. Ignorance of Hashimoto’s autoimmunity
  4. Lack of regular (or any!) thyroid ultrasound testing
  5. Lack of testing for Free T3 and Reverse T3 levels
  6. Lack of referral to an endocrinologist who understands

Now for part five …

Issue 5: Lack of testing for Free T3 and Reverse T3 levels

When I recently obtained my own record of Thyroid test results since 2013, and graphed my TSH, T4 and T3 hormone levels, I saw how many times my results were below or above lab ranges, and I was shocked.

The most disturbing pattern to see was that my T3 levels were consistently below range, despite any adjustment to Synthroid dose, and my TSH numbers were not telling the full story of my “tissue hypothyroidism.”

  • See my post on this topic: My experience with Low-T3 on Synthroid.

Since T3 is the most important thyroid hormone for cellular function, why aren’t hypothyroid patients routinely tested for levels of the ACTIVE hormone T3?

The answer is that doctors are given incomplete information and illogical policy advice about T3 measurement.

Doctors are told they can assume that the TSH (Thyroid Stimulating Hormone) will tell them if your T3 and/or T4 is dangerously low. They have been told that there is a perfect feedback loop between TSH and bodily levels of T3.  In fact this is NOT TRUE, because:

  • TSH is secreted based on T4 and T3 levels in the pituitary gland only. The pituitary converts T4 into T3 at its own rate. The pituitary T3 levels are not representative of T3 levels elsewhere in the body.
  • High levels of T4 will suppress the TSH even when T3 is pathologically low.  Patients whose thyroids have been removed due to cancer are commonly prescribed a TSH-suppressive dose of T4 (Synthroid) because it is believed that the secretion of TSH may stimulate cancer growth.

Doctors are also told that T3 testing is unreliable because of “the short half-life of T3.” It is true that T3 has a short half-life, as short as 12 hours, in the blood stream. However, this is no reason not to test for T3, because:

  • The majority of our serum T3, at least 60% of it, comes from continual T4-T3 conversion in the liver, not from direct secretion from the thyroid gland.  T4-T3 conversion occurs every minute of every day within the liver and is released into the blood.
  • Any small variation in T3 levels could be due to daily 10%-20% variation in TSH (Thyroid Stimulating Hormone) levels. The highest secretion of TSH normally occurs shortly after one goes to sleep. This means that during the night, the thyroid will secrete more hormone, about 85%-90% T4 and 9-15% T3.Therefore, on a stable daily dose of T4, TSH should theoretically also be stable from day to day, and therefore one’s daily cycle of T3 secretion from the thyroid will also be stable over many days, weeks and months.

    If you always get your blood tests done between 8-10 AM, it is unlikely that you will encounter any noticeable variation in T3 serum levels due to the half life of T3 or the diurnal variation of TSH.

Therefore, the T3 test itself is not unreliable because of “the short half-life of T3.”

Many other hormones have an even shorter half life than T3.  That does not mean they are not worth testing.  For example, the half-life of insulin is 4-6 minutes. It degrades within 1 hour of being secreted from the pancreas. Should we not bother testing insulin because of its short half-life?

Doctors are told they can assume that whether or not the thyroid is secreting sufficient T3, the liver, kidneys, and cells are converting T4 into T3 at the proper rate to supply all bodily tissues.  They assume that there is no dysfunction in conversion rate to make up for any deficiency in thyroid gland secretion rate.  However, it is well known that many factors can interfere with T4-T3 conversion. It cannot be assumed that T4-Synthroid is being converted into T3 at the “normal” rate one expects.

Doctors are also told that T3 levels can be “hard to interpret.” It is true that T3 can vary based on a person’s intake of medications or dietary nutrients that conflict with thyroid hormone production or conversion, and T3 may vary based on chronic illnesses that can reduce T4-T3 conversion.

However, the difficulty of interpreting T3 levels is a separate issue from the importance of measuring it. It is crucial to know if serum T3 is pathologically low, whatever the reason, because every cell in our body needs it to function. Serum T3 is crucially important because certain organs (like the heart) cannot convert sufficient amounts of T3 within their own cells.

If T3 is too low, then the next question to ask is WHY it is low.

Testing T3 without knowledge

Doctors are taught to test only TSH and T4 and adjust the Synthroid dose based on those results in order to “normalize” the TSH within lab range.

Doctors are not given any guidance on what to do with T3 levels if they decide to measure them, because the authorities (i.e. endocrinologists, health care organizations) do not recommend testing T3, as explained above.

Although I had asked my doctor to test “T3,” she did not know which T3 test to order, so we were ordering Total T3 for a while (which is better than not testing T3 at all, but it does not say what is freely available in the bloodstream, not bound).

When my doctor got the T3 lab results, she obviously did not know what to do with the information.  It was clearly below lab range.  But what does it really mean if my Total T3 is consistently below range?  Did I have any telltale symptoms of hypothyroidism while being low T3, that might go away if we addressed the low T3?

I received no comment or education from my doctor on my low T3.

Testing for Reverse T3

Our bodies continually convert T4 into a certain ratio of T3 and Reverse T3. By manufacturing Reverse T3, our body ensures that we don’t get an overdose of T3 and that we don’t have an excess of T4 building up. However, too much Reverse T3 can have unwanted negative effects:

  • Reverse T3 blocks cellular hormone receptors for T3, which is bad if you already have low T3 serum levels.  The T3 hormone may be in your blood but can’t get into as many cells.
  • The presence of Reverse T3 further reduces the rate of your body’s conversion of T4 to T3, which is bad if you are not converting enough T4 into T3.
  • It takes longer to clear Reverse T3 from one’s system than to clear T3, and as a result, Reverse T3 can build up over time if one’s body continues to produce it at a higher rate than it can be cleared. This is a problem if a patient is prescribed higher doses of T4 in order to resolve a Low-T3 issue in the presence of RT3 excess.  Increasing T4 in this state will increase serum RT3 levels at a higher rate than serum T3 levels, and even more T3 receptors will be blocked.

Since Reverse T3 looks like T3 at the molecular level, it is included within T3 lab test results.

Therefore, to understand how much Free T3 is actually Reverse T3, you need to test specifically for Reverse T3.

Over all these years, my doctor also never tested for Reverse T3, if she even knew she could or should. And likewise, I doubt my doctor would have known how to interpret its results.

A few months ago, in December 2015, I decided to request the Reverse T3 test and Free T3 test through my naturopath, since I knew I could order the test through their prescribing doctors.

I found out it cost me $56 to order the test through my provincial health care’s normal lab, since they had to ship my blood down to California to have this test run. (FYI, for those who live in the US, know that it is unusual for Canadians, who are all covered by provincial health insurance, to have to pay out of pocket for any medical tests ordered by a doctor).

The importance of the T3: Reverse T3 RATIO

It’s important to know that it’s not the numerical result of Reverse T3 in relation to the lab reference range that matters.  It is the Free T3 : Reverse T3 ratio that is a key signal of health or a dysfunctional T4-T3 tissue conversion rate.

  • Section on Reverse T3 from National Academy of Hypothyroidism article “Thyroid Hormone Transport”
  • Stop the Thyroid Madness website page on Reverse T3 and RT3-ratio

Do doctors even have time and knowledge to make the calculation of the fT3/RT3 ratio?

Once we get our Reverse T3 test results here in Canada, often after a 2 week delay, the two test results are not even in the right units to enable easy calculation (fT3 is reported here in pmol/L, but RT3 is reported from the US lab in ng/dL).  Even if a doctor were to do the calculation correctly, do they know the optimal fT3 / RT3 minimal ratio?

Why aren’t we always given a copy of our lab results?

And why aren’t patients normally given a printout of their thyroid test results so they themselves can become aware of, and actively participate in, their own body’s medical treatment?  We should be able to calculate our own ratios.

Students get report cards. Why aren’t patients given their test results the same way?  It’s my body. I have the right to know how it’s performing on the tests.

When a cardiologist recently offered me a copy of my lab results going back to Oct. 2013, I was overjoyed and relieved to have them in hand. What a treasure. However, I had to sign a release form to walk away with them, which showed that it was perceived as a risk for them to give them to the patient without this signature.


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