I recently got lab results for total T3 (which was at the literal bottom of the range), but it's been advised that what I really need to know is the Free T3 level, which the doctor won't order.
Is it possible to have low total T3 but a normal Free T3? The only time I ever had Free T3 measured, it was higher than my total T3 (felt very unwell at this time):
T3 Total: 89 (80 - 200)
T3 Free: 3.03 (2.00 - 4.40)
How could this be? Any insight appreciated!
i wonder if it might be something to do with the fact that only very very tiny % of total T3 is ever free T3 ... must of it is 'bound' .. not free. maybe that explains how the free T3 could be in the middle of it's range at the same time as the Total T3 can be low in it's range
if you see what i mean .. but that's a bit of a guess... we don't see them both together very often, so we don't get to see what's usual.
Well, you only have to look at the ranges to see why. The TT3 range is vast. The FT3 range is much narrower.
TT3 - Total T3 - is exactly what it says. It's the total amount of T3 in the system, both bound and unbound (free). So, if you just measure the bit that's Free, and use a much narrower range, it's not difficult for the percent of the FT3 to be higher through the range than the percentage of the TT3. That's how I see it, anyway. 
Thanks so much greygoose ! If you have a moment, would you mind checking out my reply to Jonathan below? I know you are very wise on these matters 
Can I assume that if the TT3 has dropped, the FT3 probably has too??
No, you can't assume that, I'm afraid. Although if symptoms are returning it very well could be that your FT3 has dropped. Did you have your FT4 tested? What are you taking and how much?
Possible your doctor won't test FT3 because he doesn't really understand T3 at all and wouldn't know how to interpret the results. That often happens.
They did test FT4; TT3 was 76 (76 - 181), FT4 was 1.0 (.8 - 1.8) and TSH was 1.97 (.40 - 4.50). In January, TT3 was 107, FT4 was 1.1, TSH was 2.29 (same ref ranges). My FT4 has never been above 1.1, even with increasing dosage.
These recent results were with taking 22.5 mg of NP Thyroid. Since the test about two weeks ago, I've increased to 30 mg, but really don't feel much better.
I'm certain that they don't understand T3 or thyroid at all! I was extremely anxious when I went into the office last week (about health anxiety issues) and they told me they think I should reduce my dose because I've become clinically hyper....
Ah, you're taking NDT. But such a tiny dose! Your TSH is saying that you are under-medicated, which isn't surprising. Usually, on NDT/T3, the TSH will be very low - suppressed, even. And, on NDT, it's perfectly normal that your FT4 stays low.
I'm certain that they don't understand T3 or thyroid at all!
No, they don't, that's true. But, they think they do understand the TSH, and that it tells them all they need to know. However, they know they don't understand T3, that's the difference.
they told me they think I should reduce my dose because I've become clinically hyper....
Oh, what rot! What does that even mean, anyway? lol
Lol, right??
Usually, on NDT/T3, the TSH will be very low - suppressed, even. And, on NDT, it's perfectly normal that your FT4 stays low.
So are you saying it is likely that to feel well, and have FT3 and FT4 where they need to be, my TSH on NDT would likely be lower than 1.97?
Is it normal that the FT4 stays low because there is not as much of it in NDT compared to taking straight Levo? Is raising FT4 also important to feeling better? Because I understand that T3 is the active hormone...
I'm most definitely saying that, yes. Quite a bit lower. But, it's not about the TSH. The most important number is the FT3.
Well, I wouldn't have said that there wasn't much T4 in NDT, there's usually around 38 mcg T4 to 9 mcg T3, so a huge difference. But, taking T3 will almost always lower FT4 levels.
And, that is fine for some people. We're all different. But, even though T4 is basically a storage hormone, and T3 is the active hormone, some people do need quite high levels of FT4 to feel well, and have to add levo to their NDT.
At the moment, you cannot know exactly what you need in the way of either, because you are under-medicated and need to try a higher dose of NDT. Get your FT3 up a bit first. You can worry about the FT4 later.
Thanks so much for your help! Now to find out how to get my hands on a higher dose to try.....
One last question--I didn't realize the timing of your last dose with NDT and testing was different than straight Levo. My latest labs were drawn 24 hours after last dose. I usually take it as one dose in the AM. Next time, I should split NDT the day before, so that I take half in the AM and half ~12 hours before the draw?
Ahhhhhh ok! So perhaps you're not as under-medicated as all that. However, that would only affect your FT3 level, not the TSH or the FT4. So... who knows! lol We'll see next test.
Yes, split your dose and the last half should be 8 to 12 hours before the blood draw.
Thank you for the recommendation and insight!
I am still a bit at a loss, since my doctor won't order the Free T3. My latest TT3 on July 14th was 76 (76 - 181) and FT4 was 1.0 (.8 - 1.8).
Six months ago, when I did feel a bit better after starting NDT, my TT3 was 107 (76 - 181) and FT4 was 1.1 (.8 - 1.8).
I'm just wondering if I can use that TT3 as a reference whatsoever for adjusting my dosage. Can I assume that if the TT3 has dropped, the FT3 probably has too?? I feel like crap and can't tell whether I need to up the dose, lower it, or focus on vitamins, etc. This is so frustrating!
Effects of low normal T3.
normal TSH and T3 but Low T4
high T4, Normal TSH, lowish total T3, rising Lipoprotein(a) 
TSH extremely low but low-ish free T3 and free T4
