Is high t3 a sign of reverse t3?

[Pearl1981]

Please explain to me the difference or whether they're the same thank you so much

[greygoose]

No, it isn't.

T4 (levo) converts into two types of T3 : normal T3 and rT3. That is done by removing one iodine atom from a molecule of T4. I can't remember the percentages, but both T3 and rT3 are produced all the time. However, under certain circumstance - illness, famine, etc. - more rT3 is produced in an effort to reduce energy consumption. This is done by removing the 'wrong' iodine atom, so that the rT3 molecule is a mirror image of T3 - hence the name : reverse T3. The rT3 molecule cannot get into the cells, meaning that the body has less T3 and therefore has to slow down. This is a normal safety procedure to preserve life.

But, there is another reason for the body producing excess rT3. When you have a 'conversion problem' as we say, when the body has difficulty converting to T3 normally, and the FT4 level reaches above a certain point, the body will start converting it into rT3, so as not to waste all that T4. Because the rT3 is then converted into T2, so it's more economical, as it were. But, in that case, you would have high FT4, but low FT3.

If you have a high FT3, but still have hypo symptoms, you have an absorption problem - the T3 isn't getting into the cells. But, that's something entirely different, and nothing to do with rT3.

I'm sure that's as clear as mud, but I hope you get the gist!

[shaws Administrator]

This is an excerpt from the following link:

Old studies show that on average, most people convert more than 50% of their T4 to reverse T3; correspondingly, they convert less than 50% of T4 to the metabolically active hormone T3. And the levels of reverse T3 fluctuate up and down through the day. Because of this, I’m never confident of coming to a conclusion that someone has a problem with high reverse T3, not unless the person has had multiple measures of the reverse T3 over a 24-hour period. Like the TSH, free T4, free T3, reverse T3 levels vary dramatically every 30 minutes or so. Depending on when a person’s blood is drawn or saliva taken. Sometimes the levels will vary enough so that a clinician will give the patient a different diagnosis from the one that he or she would have given 30-minutes before or after the blood or saliva sample was taken.

So blood levels vary rapidly. Because of this, I don’t believe the reverse T3 or the other lab tests in general are very useful. However, I do believe the reverse T3 is useful under one circumstance: when we have enough measures to get averages over time, and when the levels are regularly way out of range. So, in my view, the reverse T3 can be useful, but I think its usefulness is limited, which is true of the TSH and other thyroid hormone levels. >>>

toopoopedtoparticipate.com/...

[jimh111]

There are two deiodinases that convert T4 - D1 and D2. Not all cells express D1 and D2, some have neither.

D1 takes place near the cell membrane and converts equimolar quantities of T4 to T3 and rT3. rT3 is inactive but it enters the cells and binds to receptors, thus blocking the activity of T3. D1 activity increases when fT4 levels are high, such as during hyperthyroidism. It is thought D1 acts to conserve iodine in these situations by converting T4 to the smaller T3 and rT3 molecules which are easily reabsorbed in the gut.

D2 takes place deep within the cell close to the nucleus, it converts T4 to T3. D2 seems to be upregulated by low thyroid hormone levels and high TSH. Amongst other cells D2 is expressed in the brain and heart and has a role in maintaining correct T3 levels in these organs.

For completeness there is also D3 which converts T4 to rT3 and T3 to T2. D3 is upregulated when thyroid hormone levels are high.

An fT3 blood test measures 'free T3', the small quantity which is not bound to serum transport proteins. An rT3 blood test measures the total amount of rT3. You can't compare the two, one is the tiny 'free' portion and the other is the large 'total' quantity. Also, rT3 has a much shorter half life than fT3 (a few hours v 24 hours), so blood levels will not reflect the actual quatities produced.

To answer your question the relationships between fT3 or tT3 and rT3 are so complex that it is no use trying to infer rT3 levels from fT3 or tT3 levels. The extract Shaws quoted from an article by Dr John Lowe sums it up. Unless rT3 levels are very high there is no value in looking at them, we can't turn the numbers into meaningful analysis, doctors who dream up magic ratios are either pushing for business or bad scientists.

[Mikegov in reply to jimh111]

Does your reference to "magic ratios" include the T4/T3 conversion ratio?

[jimh111 in reply to Mikegov]

Yes it does! In a healthy person the fT4 / fT3 ratio will vary with the levels of the individual hormones. The two levels tend to 'see-saw' as fT4 rises within its reference interval fT3 tends to fall or remain steady. Both T4 and T3 contribute to thyroid hormone action as many tissues are able to convert T4 to T3, especially the brain, heart and brown adipose tissue. Also it looks like the amount of T3 these tissues release into the bloodsteam varies very considerably.

In terms of ratios, it would only make sense to look at total T4 and total T3 since this reflects how much T4 has been converted to T3. However, you don't know how much has come from type-1 deiodinase (which also produces rT3) and how much has come from type-2 deiodinase.

So, you can get a rough idea from looking at TSH, fT3 and fT4 but it is bad science to calculate ratios as this suggests there is a mathematical accuracy in the result.

[Pearl1981]

Thank you for all of the answers. I'm asking because on my last blood test I had high free t3 and uper range free t4 . However I had taken my medication that morning . Ifound this excerpt and I'm wondering why I'd have the high ft3

"TSH & free T3 are the same whether you take your T4 medication before or you have waited up to 48 hours to take the blood test. T4 peaks 2 hours after taking it in medication, so can affect a blood test when taken during that peak time. Most of the rest of the day, the T4 levels will be stable."

My last blood test around 3 months ago

T4 free 1.09ng/dl (0,61 - 1,12)

T3 free 8,2 (2,3 - 3,9)

TPO 0.8 (0-9)

Ferritin 96,3ng/ml (11-307)

B12 822pg/ml (134-590)

25 OH D 82,92ng/ml (39-100)

Usual body temperature now on 4 grains: 37.4c

I have increased my dose from originally two grains to four grains in a 6 month period.

On two grains I had crushing fatigue , dry skin, constipation, puffy face and hands, swollen joints, hair loss and eyebrow loss. Also had low body temp of 36.0c.

I do feel better now but still get tired sometimes and have some dry skin.

Just wondering why I have such high ft3

[Pearl1981]

Anyone?

[helvella Administrator Thyroid UK in reply to Pearl1981]

We always point out that thyroid hormone tests will be higher in the hours after taking the tablets.

However I don't know if FT3 being quite that high is what would be expected.

[Hidden in reply to Pearl1981]

Your FT4 levels are close to the upper normal limit. If you convert some or most of it to T3, you could end up with too much T3 along with the T3 naturally present in NDT. It's usually recommended to have FT4 levels low in range or at least no higher than midrange when on NDT.

[Pearl1981]

am I over medicating?