Would you test ft3 6-8 weeks after being on the desired dose of t3 medication to see if you are optimal or need to increase?
Ft3 test: Would you test ft3 6-8 weeks after... - Thyroid UK
Ft3 test
Written by
PinkSkittles
To view profiles and participate in discussions please or .
Read more about...
59 Replies
•
Hi PinkSkittles
Six to eight weeks should be fine for a blood test, but I would say you will know when you are on the right dose when you feel well. Sounds a bit glib I know, but it is all too easy to get sucked into the numbers game so wholly that we can miss consideration of the alleviation of symptoms. How are you feeling right now. Have you found your sweet spot ? 🤗
I've been on 31.25 mcg for 2 weeks and don't feel any different. So I guess I'd increase after 6-8 weeks.....
RegenallotmentAmbassador
yes I would 🌱 it really helps build a picture, my pharmacist adviser at Roseway Labs prefers 12 weeks, but personal observation is I can see what is what at 6 weeks. I am more 'settled at 12 but if I'm low, then I'd prefer to know 6 weeks earlier rather than waiting for the inevitable, if I am high it will show 🌷
Do you mean you prefer to know at 6 weeks if ft3 isnt high enough and you need to increase t3, rather than waiting for 12 weeks?
yes.. thats what I meant 🙂
Okay thank you
Agree with above.
Rule - 6 to 8 weeks minimum. Like, don’t even bother testing before 6 weeks : )
If you know you are still under replaced (like those on starter or low doses) then 6 weeks is fine.
The closer you get to what appears to be your sweet spot, then it never hurts to wait that 8-12 weeks.
I’ve read many posts here - especially while panicking in the middle of any particular titration period - about things distinctly settling after those additional weeks. Like, week five is nuts but week six feels more settled then by weeks 8+ it again can settle even more.
I’ve experienced it myself, and more to the point, as I am a true believer in “low and slow” - I’ve taken a full 6-8 weeks to increase by 12.5 Levo, then another 6-8 for a second Levo increase of just 12.5.
Smooth sailing compared to higher and faster titrations in the past.
Edit - I've been on 31.25 mcg… what did you increase FROM?
hey PinkSkittles i read a comment on another post that made me think there is more to the T3 approach.
I know that T3mono is different.
But I do hope someone comes along to add some nuance here…. In my experience I had felt the difference of low and slow increases over the weeks with T4, and also the shock of adding too much T3 all at once and waiting months to settle. I do indeed practice what I posted above.
But let me know if you find out or conclude anything else.
Hello pinkskittles,
My response to your question is 'it depends'. I am though an advocate of increasing 'low and slow' How slow depends on other factors. I am also an advocate of having some T4 from your thyroid or from medication if possible. This is because it provides a reservoir of T4 from which to make T3 if your body needs extra T3. Understanding what is happening in your body is key.
For example, to take one extreme, I have a completely atrophied thyroid that produces no thyroid hormones and my thyroid does no T4 to T3 conversion. The T4 to T3 conversion done by the rest of my body is very poor, my conversion rate being 0.18, whereas Midgley et al in their research 'variation in biochemical response to l-thyroxine therapy and relationship with peripheral thyroid hormone conversion efficiency' said a poor converter is less than 0.25. (Actually they say 0 23 but their result is in different units to mine.) I am allergic to levothyroxine. I am therefore on T3-only thyroid medication. I am not saying T3-only is best, just that I have no other choice. In this situation, with no T4 to complicate matters, when I first went on T3, I increased by 5mcg T3 every 5-7 days, and had a blood test every 10-14 days. Due to the short half life of T3 it is ok to increase every 5-7 days. It took my body 5 days to adjust to each increase, I knew it had adjusted because the symptoms I experienced at the increase settled down after 5 days.
If you are taking T4-only, T4 +T3, or have a partially working thyroid that produces some T4, then the situation is different. This is because T4 has a longer half life. This means it lasts longer in the body. As a result, any blood test taken before 6-8 weeks will not show the settled down result. In the meantime, your body is adjusting your T3 and T4 levels to accommodate the T3 that you are getting from T4 conversion as well as the T3 tablet you are taking. (Deiodinases are important here. My understanding is that Dio1 and Dio2 govern how well you convert T4 to T3, and Dio3 governs how fast your body gets rid of T3 if there is an excess.)
In summary, if you are on T3-only with no working thyroid, a blood test after 7 days will show the correct levels. If you are taking some T4 or have a partially working thyroid, then the blood test after a minimum of 6-8 weeks will show the correct levels.
Thank you for this explanation. I've increased by 6.25 mcg every 5-7 days. Ive been on 31.25 mcg for 2 weeks and don't feel any different. Im on a little bit of t4 only 50 mcg.
per my post above
healthunlocked.com/thyroidu...
Feeling are one thing… but still conventional forum wisdom to wait 6 weeks after a change before bothering with a test.
(T3 mono is entirely different)
Agree
As a rule of thumb, I use 15mcg T4 is equivalent to 5mcg T3, i.e. a ratio of 3:1. Not the ratio of 5:1 usually quoted. I read the 3:1 ratio in research somewhere but have no idea where. Using 3:1, this means your 50mcg T4 is equivalent to approximation 17mcg T3. 17 + 31.25 = 48.25mcg T3. If one have any thyroid fuction left, this may be sufficient T3. If no thyroid function left, it is unlikely to be enough as at least 60mcg is usually needed. This may be the reason you don't feel much different.
Are you tracking signs, such as blood pressure, heart rate, and temperature to monitor changes, as well as symptoms? If not you are likely to find it beneficial to do so.
Hello that is really kind of you to work that out for me thank you! I have such low mood and chronic fatigue and feel so hopeless so I appreciate it.
I havent done any tracking of obs no- partly because I find it all so overwhelming ie what kind of thermometer can you use? Can you rely on the readings and believe that they are accurate.
Also Id need some simple instructions to follow. I research everything myself and very thorough with my reading but it all gets too much looking up everything all the time.
Also would you still wait 6 weeks to increase again or do it now as I dont feel better yet?
Could you use your resting pulse rate as one of the measurements? I used to measure my pulse/ heart rate at night after I'd been lying down for 30 mins. Below 60 I was under-medicated above 80 I was definitely overmedicated. Oxymeter is the easiest way to do this if you don't feel up to measuring your pulse yourself.
I use a Braun ear thermometer.
Thank you. What temps are we looking out for? Do you think I should increase again or wait?
T3 has a half life of 1 - 2.5 days. It takes ~5 half lives to reach a steady state so long as your dose is constant. So to test only FT3 levels you'd want to wait about 2 weeks (2.5 X 5 = 12.5 days) to determine your new FT3 level.
For T4, the half life is 7 - 10 days. 10 X 5 = 50 days, which is ~7 weeks, hence the usual 6 to 8 week wait to determine new FT4 levels after a dose increase.
Be sure that when you do your test that you've allowed the same duration of time between the last thyroid dose containing T3 and the time of the blood draw.
Thank you for your reply.
2 weeks! Ive never heard that before. So why do people say 6-8 weeks normally?
Sorry I dont understand your last paragraph.
Because while the bit about five half lives or so is widely accepted as a theoretical approach. But in thyroid issues everything interacts in complex ways. A change to T3 dose interacts with TSH secretion and T4 levels.
Okay sorry so meaning what exactly?
Nothing exact about it. That IS the problem.
A change in T3 will affect TSH and T4. They will change.
And if T4 changes, you have to look at seven weeks.
Much of the adjustment might occur more quickly but those changes ripple on like waves on a pond.
Okay gotya
So if I dont feel any different after being on 31.25 mcg for 2 weeks would you increase again now or still wait for 6 weeks?
Are you only on T3?
The reason for waiting longer for products containing T4 is that it takes more time to reach a maximum blood level. You don't want to increase a dose until you're fairly certain you've reached that peak. You can overshoot an adequate dose that way. For T4, that can be 6 to 8 weeks, which also affects your T3 blood level, since you'll continue to convert more T4 to T3 throughout that same period.
If you're on T3-only, then you can raise a dose more quickly because you'll reach the maximum blood level (on a given dose) within 2 to 3 weeks.
If you're taking desiccated thyroid, the dosage and administration is clear:
Armour Thyroid Patient Package Insert
"Therapy is usually instituted using low doses, with increments which depend on the cardiovascular status of the patient. The usual starting dose is 30 mg Armour Thyroid (thyroid tablets, USP), with increments of 15 mg every 2 to 3 weeks."
Despite the fact that Armour contains both T4 and T3, the recommendation is increasing at 2 to 3 week intervals. If you're concerned about FT4 and FT3 blood tests results though, you'd want to wait 6 to 8 weeks.
"Because while the bit about five half lives or so is widely accepted as a theoretical approach. But in thyroid issues everything interacts in complex ways"
"Nothing exact about it. That IS the problem."
The administrator is correct. There is no exact time or exact treatment guideline. That's why it's not exactly 6 weeks and not exactly 8 weeks. You won't necessarily get well when your TSH is 1.0 or your FT4 and FT3 are at a certain level. Other factors are involved in how long a drug is effective and remains in the body. There's also the genetics, whereby someone might not see improvements due to cell receptor down-regulation, causing temporary resistance to thyroid therapy. Cortisol plays a role in how well a thyroid dose works. It's complicated.
Bottom line is, all you can do is try. All progress comes with some risk. Raise the dose incrementally. Monitor your blood pressure and heart rate and log any symptoms, especially those of overstimulation. And evaluate thoroughly your vitamin and mineral levels just to rule out that this is what's causing a lack of improvement.
Hi Im on 50 mcg of t4 and 31.25 of t3
Thank you for your reply. How do I monitor bp and hr? What am I looking for?
Normal blood pressure is considered to be 120/80. Thyroid hormone (T3) will raise blood pressure. If you're taking too much thyroid hormone, then you'll see a measurable increase in your blood pressure, along with some unpleasant symptoms like sweating, palpitations, fast heart rate.
Do you own a blood pressure monitor? Create a log and record your BP and heart rate daily. Make notes on whether you begin to feel agitated.
Example of a blood pressure screen
Thank you. Yes i have a bp machine so i can do this.
Also I didnt understand the last paragraph of your 1st comment:
"Be sure that when you do your test that you've allowed the same duration of time between the last thyroid dose containing T3 and the time of the blood draw."
Hi again! How often would you increase t3 if no change in symptoms? It will be 2 weeks of being on 31.25 mcg and I feel exactly the same- dreadful.
Can you give me an idea of how you're dosing the thyroid medication you're on now? I'm assuming you're taking 50mcg of levothyroxine in the morning. Are you spreading the T3 throughout the day? If you're taking T3 all-at-once, you might find that this won't maintain a minimum therapeutic blood level. Despite some people taking it all in one go, not everyone metabolizes thyroid hormone the same way.
Do you have any test results for cortisol levels? You might want to record your body temperature to see if you have any sort of adrenal dysregulation. Low temp but steady tends to be thyroid related; unsteady temp throughout the day tends to be adrenal related. Low and unsteady...thyroid and adrenal wacking you from both sides.
It would also help to know the top 10 symptoms you're experiencing.
Screenshot of body temperature readings
Thank you for your help! I really really appreciate it!! I'm feeling sooooooo terrible.
I will answer in separate messages as its too overwhelming.
Timetable:
9-9.30am: 50mcg t4 + 12.5mcg t3
3-3.30: 12.5 mcg t3
9-9.30pm: 6.25 mcg t3
I dont have any recent cortisol results.
I can record my temps like you said. Ive not done that before. Can I send them to you here after? Im too overwhelmed/brain fog/low to work them out myself.
What thermometer shall I use and what body part? All body parts have a different reading so how can you trust them? I have a digital thermometer here.
I use a digital thermometer placed in my mouth. The trick is to find one that is consistently accurate. A mercury thermometer can be used although I'm not sure if they're still sold. I was measuring basal temperature under my arm but I broke that mercury thermometer (because I actually fell asleep while doing it) and decided not to go that route anymore.
Mercury thermometers were banned from sale many years ago.
There are thermometers based on gallium (or gallium alloys) which work the same way but can be difficult to shake down after use.
Spilled mercury is one reason for their being banned. Some parts of health facilities have been significantly contaminated by mercury - typically from thermometers being broken when accidentally released during shake down over many years. Remains giving off mercury vapour for a long time.
Right. While I wasn't actually recommending using them (because of my own experience) I can see how my comment could be misinterpreted.
I don't think I did misinterpret!
I started by just confirming they are no longer available. Offered a pointer to a similar alternative. Then, from long experience of posting and replies, realised that even if not recommended, or even disrecommended!, someone was likely to say "I don't know why they were banned. Wish we could still buy them." So tried to pre-empt that by adding a general explanation. 
How do you know if they are consistently accurate?
By taking your temperature every couple of minutes for 3 or 4 readings. If the temperature jumps up or down significantly during that time, the thermometer may not be that consistent. I would guess that on this forum there might be people who've found good digital thermometers and I would consider their recommendation.
Ahh okay thank you for explaining
Top symptoms that stop me from functioning normally:
- Can't work (not a symptom I know)
-Wake up feeling hungover
-Depressed
-Chronic fatigue
-Brain fog/executive dysfunction
-Nervous system dysregulation/feel very overwhelmed/stressed
-Aching heavy eyes
-Period issues: pain and feel extremely drowsy/mood difficulties and very fatigued
Other symptoms but they dont stop me functioning/living my life:
-Get cold very easily. Often need a hot water bottle. Cold hands and feet
-Internal tremors sometimes
-Red, hot, achey knees when I bend them
-Aching all down my legs (need to take pain killers) even when I havent been outside for a walk
-Dont empty bowels every day
How would you rate your sleep? Are you able to sleep through the night? Do you get the amount of sleep you believe you need?
I find it very hard to get to sleep because Im tired but wired.
I zleep through the night.
I find it very hard to get up.
A sleep study showed I have poor quality sleep. Delayed rem sleep and not enough episodes of rem. It also showed that my sleep is very disrupted turning over all the time.
It sounds like you may have elevated cortisol levels at night and lower-than-ideal levels in the morning. What was your total sleep (hrs, mins) in the study?
I did a saliva cortisol test back in 2017 when I was experiencing all these symptoms like I am now. It came back high at points 1,2 and 4. I got it back down to normal with phosphatidylserine and felt exactly the same!!
I dont remember the number of hours I slept during the sleep study.
Could you be sensitive to fillers in your t4/t3 medication? Your symptoms sound like the ones I experienced, before finding out that the make of Levo I was on was causing my problems. I have since had the make changed and feel better for it. I was experiencing Migraines, heavy legs (like walking through water) face looking like I had allergies - puffy etc. Your heavy eyes could be a sign of an ongoing allergic/sensitive could be a possible reaction to one of the fillers in your t4/t3. Not saying it is, just wondering.
Do you mean the symptoms I listed above? Ive had them since 2015. Some before then but much more mildly. I only started t4 last year.
Yes. My brain must have skipped the bit about how long you've felt like that. I just thought that the symptoms you described sounded familiar. Sorry.
Ps following advice from other people here I am going to stay on 31.25 mcg t3 for another 4 weeks, retest and see if I need to increase.
Im also going to buy a fingerprick test to do next week to make sure my ft3 hasnt gone up too high, as the speed I increased, whilst recommeded by my Dr, is apparently too fast for some people. I havent had any symptoms of heart racing or feeling hot though.
Any other thoughts or advice on my replies would be gratefully received. Thank you!
I would recommend during that time to record any symptoms that you have. Some can be constant while others can be intermittant. You´ll be able to see the improvement much more clearly by being able to look back through your log book. An example:
Screen shot showing a list of thyroid and adrenal symptoms
In order to evaluate blood testing accurately, and since the FT3 levels drop rather quickly, it's important that the time between taking your last dose the previous day and the time of the blood test the next morning is the same.
First set of thyroid blood tests:
March 7th, 2024 Time of last dose: 5:00pm
March 8th, 2024 Time of blood test the next morning: 7:00am
Time duration: 14 hours
Second set of thyroid blood tests:
March 28th, 2024 Time of last dose: 5:00pm
March 29th, 2024 Time of blood testing the next morning: 7:00am
Time duration: 14 hours
Most people on this forum prefer to measure their trough (lowest) thyroid levels versus their peak(highest) blood levels. The importance of this would be to gauge how long a particular dose lasts in their therapeutic range. Waiting 14-15 hours will give you the lowest FT3 reading.
Let's say that you've determined that an optimum dosage of thyroid hormone will put your FT3 blood levels at 5.8 pmol (range 3.3 to 6.8). You'd want to make sure that when you take your thyroid medication, the FT3 blood level never drops below 5.8 pmol during the day. If by testing ~ 15 hours after a thyroid dose you discover that your FT3 blood level is 4.2 pmol, you'd know that this is less than what you need. So the dose would be raised.
To determine your peak FT3 level, you'd want to take a dose of thyroid medication about 4 hours before a blood test. This would show you how high your FT3 level actually goes. This is also important to know because if your dose causes you to reach (for example) 7.6 pmol at its highest, depending on how long the level stays above your upper limit, this could cause symptoms of overstimulation and long-term side effects.
By the way, virtually nobody on this forum checks for peak FT3 levels because of the concern that their doctor (using only the TSH level) will lower their dose (he definitely would), thinking that they're hyperthyroid when they're not.
Thank you so much for explaining this!!
Not what you're looking for?
You may also like...
FT3 / T3 test
Looking on Medichecks site for tests.
Please can anyone explain the difference between the above...
FT3
Hi,
Could anyone tell me how do you know if you would benefit from FT3 .I have always been on...
Antibody Test results and FT3, FT4
Hello everybody. Thanks for your recent help. I got the tests that you suggested done and these are...
FT3
I have no thyroid. FT3 range is 3.5-6.5. Wondered how much FT3 I should have. Last test was FT3 at...
TSH/FT3/FT4 Test Results
Hi,
Hope everyone is doing okay. I just had these results back:
TSH 0.05 (0.2 to 4.2)
FT3 4.17...
FT3 range
Thyroid Test - no FT3 by GP
FT3 testing.
FT3
High FT3 
