Thyroid Thursday Episode 27: Reverse T3 Part 3 – Does normal TSH indicate normal rT3?
Today I want to continue the discussion from the last two weeks regarding reverse T3. There was a question that was asked; does normal TSH indicate normal reverse T3 levels? A viewer asked their endocrinologist to run their reverse T3. They’ve been watching a number of the videos. They are still having hypothyroid symptoms even though they are taking Synthroid and they asked their doctor to run their reverse T3. The doctor said he didn’t need to run reverse T3 because as long as the TSH was normal, that indicated that the cells were getting plenty of T3 and therefore reverse T3 would be normal. But that’s not really true.
Let’s have a little review and we’ll talk about what some of these things mean and I’ll give you an explanation of why that’s not true. TSH represents the T3 levels in the pituitary gland. How does this work?
When there is stimulation in the body, T4 is converted to T3 by an enzyme called deiodinase 2. In the pituitary gland, the only enzyme that really is present for a conversion of T4 to T3 is deiodinase 2. The peripheral tissues have deiodinase 1, deiodinase 2 and deiodinase 3. The pituitary actually acts a little different in the rest of the cells of the body, which is why TSH reflects the saturation of T3 at the pituitary level, but does not represent the T3 saturation at the peripheral cellular level. Peripheral cell are the cells outside the pituitary gland. The peripheral cells act a little bit differently. They do have D2, they have D3, and they have another enzyme called D1, but D3 is the primary enzyme that converts T4 to reverse T3.
Under situations that drive up D3, the peripheral cells will be impacted. The pituitary gland does not have D3, so it can only make T3. So, if we have situations like calorie restriction, inflammation, insulin resistance, or some type of stress response in the peripheral tissues, D3 may be upregulated.
In that case, we are going to make way more reverse T3 (instead of T3) and that’s going to bind to the receptors (instead of active T3) and it’s going to cause hypothyroid symptoms. Since there is no D3 in the pituitary gland under the same circumstances, only D2 is produced and T4 can only be converted to T3, which is why the pituitary gland can become saturated, normalising or lowering TSH.
The doctor can look at your TSH value and say, “Well, you have normal TSH or it’s low, therefore the cells of the body must be saturated with T3, and therefore your symptoms can’t be as a result of low peripheral thyroid hormone status”, but as I’ve talked about on a number of videos, TSH only represents the T3 at the pituitary gland. We now know via research that TSH does not represent the T3 level and the T3 saturation at the peripheral cells.
The doctor was incorrect in telling the patient that with normal TSH, they didn’t need to run reverse T3 because it would be normal, because TSH does not represent what is happening in the peripheral cells, it only represents what’s happening in the pituitary gland, and the pituitary gland only has D2 enzyme.
There is no enzyme in the pituitary gland to convert T4 to reverse T3 to compete with T3. The pituitary gland would be looking normal. The reason you still have hypothyroid symptoms is because of the stress response on the body.
If you are taking T4 (Synthroid) and it isn’t being converted into T3, it is being converted to reverse T3 in much greater concentrations. Interestingly, when I ran a thyroid panel on this patient, her reverse T3 was greater than 24 and 24 is a lab high. In this situation, the patient’s reverse T3 was greater than 24, it was actually in the 30’s. This person was really over converting the Synthroid into reverse T3. That reverse T3 was blocking the peripheral cell T3 receptors. So, even if they were making some T3, it couldn’t get to the receptor to stimulate metabolism, which is why they still had hypothyroid symptoms.
If you are taking Synthroid or Levothyroxine and you still have hypothyroid symptoms, really work with your doctor or your endocrinologist to get a reverse T3 done. If your endocrinologist won’t do it, call an office like mine and we’ll almost always run a comprehensive thyroid panel because we want to take a look at what those reverse T3 values are.
Now, can you just take the reverse T3 as the value only? No, because somebody may still have normal amounts of reverse T3. It is not just about how much T3 you make, it’s about the T3 to reverse T3 ratio. If that ratio is less than 10, then the person has cellular hypothyroidism. They are making more reverse T3 in relation to T3. The other value we can look at is the free T3 to reverse T3 ratio and if that is less than 0.2 then the person has cellular or peripheral hypothyroidism.
Remember, hypothyroid symptoms don’t occur because the gland isn’t necessarily making T4 and T3, hypothyroid symptoms occur because the peripheral tissues aren’t getting enough T3. One of the reasons they may not get enough T3 is because of the impact of stress on the body, the body is using D3 to convert T4 to reverse T3 in the peripheral cells. The pituitary gland, which is what the doctor is looking at with just the TSH, doesn’t have D3 to make any reverse T3, so of course T4 under D2 only will be converted to T3, it will saturate the pituitary gland, telling the brain, “Hey, we don’t need any more T4, so we are going to lower TSH”. So, hopefully that helps. Look forward to another Thyroid Thursday edition next week. Take care.
