Timing of blood test when on T3 only: I have just... - Thyroid UK

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Timing of blood test when on T3 only


I have just received my blood test kit from Medichecks and it says to take the sample in the morning. I take my T3 in two doses - first thing in the morning

and then about 2.30pm. Could anyone tell me if I should take my morning dose after I've done the blood test? Will it effect the result as I won't have had any T3 since the previous afternoon. I would appreciate any advice.

11 Replies

I would take the morning dose after doing the blood test, yes. Otherwise the FT3 levels may read artificially high for a few hours after taking your liothyronine.

It's difficult with such a strange dosing strategy. I'd take the blood around 1 pm, this will give you a reasonably average result, assuming 'first thing in the morning' is before 9 am. If you take the blood in the morning before your T3 you should double your fT3 figure to get a reasonably accurate value. This will be less accurate than the first option as you can't be sure that your T3 half life is exactly 24 hours.

humanbean in reply to jimh111

jimh111 That would give Batchelor23 about the lowest TSH possible, which may not be what he/she wants. Most hypo people want to get the highest possible TSH in testing not the lowest.

Another problem is that testing should be done fasting (apart from water), but that isn't possible when the test isn't done until lunchtime.


My suggestion would be to do the test at around 8am or 8.30am, and whichever time you pick stick to that for future testing purposes. The day before take your T3 in the morning as usual and take the second dose about 12 hours before you intend to test.

On the day of the test don't take your first dose of T3 until after you've got your blood sample.

Remember to fast over night, for about 8 - 10 hours before doing the test. Don't drink anything except water (which can be drunk freely - dehydration needs to be avoided).

Please note that getting a blood sample shouldn't be done until Monday now. Doing the blood test on a Thursday, Friday or Saturday morning and then posting it would mean that the blood sat around in a post office or sorting office or at the lab for the weekend and that may reduce the accuracy of the results.

jimh111 in reply to humanbean

It depends on whether you want an accurate result or fiddled results. If you want to fiddle I suggest it would be better to get a copy of a set of results and edit in the numbers you want! Fasting before the blood test is not needed, we don't fast in our daily lives. Just behave as normal and you will get a normal result.

It makes sense to avoid taking the blood on a Friday or Saturday.

If you alter your dose to 12 hour intervals and then take the blood after 12 hours you will need to add about 25% to your fT3 result to get a realistic figure. Your TSH will also be too high but the calculation is beyond my maths nowadays.

humanbean in reply to jimh111


I think people should be aiming to get a result using a standard sequence of events that are repeatable from one test to another so that comparisons makes sense.

And you obviously know that TSH varies throughout a 24 hour period. If the OP ever wants to show results to a doctor then you also know that a low TSH will get meds cut or removed altogether. So most of us on here feel most secure when getting a result which maximises TSH.

From a logical point of view a TSH done at 8am or 10am or 2pm or 10pm would all be given the same weight and there would be understanding from doctors that TSH alters throughout the day. But since that understanding is missing, we do what we have to.

In a health system which was really logical and cared about how patients felt and whether thyroid hormones were optimal for the patient the value of the TSH would be lessened. But since we have to live in the real world, a high TSH is better for a hypo patient than a low one. And if that means having to test at certain times then so be it.

I think I remember reading that you got diagnosed hypo with a TSH between 1 and 2. My apologies if I'm wrong. I don't know how you managed it. Perhaps because you are male? Women don't get this leniency or compassion, so we have to work the system the only ways that are open to us. And I think your compassion is often lacking when you answer people suggesting they test in a way that might get meds taken off them inappropriately.

And finally - if someone is over-medicated they will eventually, one would hope, reduce their dose of meds by themselves.

jimh111 in reply to humanbean

I understand where you are coming from. First a correction, I should have said to add about 20% not 25%. In this case it is unfortunate that T3 is being taken early morning and 14:30. As an aside I have found that the nighttime L-T3 dose is most important, sufficient T3 during the night seems to enable more productive sleep and better cognition during the day.

It's unfortunate that doctors rely upon the TSH. I appreciate that some patients need to fiddle their TSH to get treatment. The problem is that if this becomes prevalent it reinforces the belief that TSH precisely reflects thyroid hormone activity, because the doctor doesn't see hypothyroid patients without an elevated TSH. Fiddling the TSH in the long run increases belief in the TSH. The question in this case is does the patient want to know their hormone levels or do they want to manipulate their doctor (or both - they will need two blood tests). I assumed that because it is a home kit they wanted to know their hormone levels.

I had severe hypothyroidism with a TSH of 1.0, I was told I couldn't possibly be hypothyroid because the blood tests said so. I was diagnosed because I saw Dr Skinner.

Batchelor23 in reply to jimh111

I am taking 30 mcg T3 and tried taking it in 3 doses of 10 mcg to begin with but felt I was struggling with fatigue again at work after a few weeks so decided to try taking the dose twice a day (20 mcg at 7am and 10 mcg about 2.30 in the afternoon). I can't say it has helped. Do you think I should revert back to 3 x 10? I don't think I'm on a high enough dose yet.

jimh111 in reply to Batchelor23

If it doesn't make a difference I suggest you revert to three times daily as this gives a more even dose similar to what happens naturally. If you are able to split the tablets you could try 15 mcg before breakfast and at bedtime. I really do find the bedtime dose crucial. With the right dose I fall asleep in reasonable time and sleep fairly well until morning. My sleep seems better quality with more 'real' dream and I feel much better the following day with better cognition. I've no scientific evidence but I think we need deep dream sleep to clear out the brain and reorganise our memory banks. I feel adequate T3 overnight is more important than during the day.

humanbean in reply to jimh111

The problem is that if this becomes prevalent it reinforces the belief that TSH precisely reflects thyroid hormone activity, because the doctor doesn't see hypothyroid patients without an elevated TSH.

It can take years, in some cases, for people to get their thyroid tested for the first time. And if TSH is anywhere within range or even below 10 then they may have to wait another year for a re-test, and then another year, and then another year.

I am not convinced that doctors are inundated with millions of patients complaining of tiredness who want a sick note to get off work or to be diagnosed with something that will get them benefits. I think the vast majority of people who go to their doctors have a damn good reason for being there. And the ones who go back and back and back really do have a problem - whether it be thyroid or caused by nutritional deficiencies or low hormones or a dozen other things. But that reason is never discovered.

In my view the problems we all have (not just the people on this forum) is that we were brainwashed into believing stupid guidelines on "healthy" food for economic reasons. We are prescribed stuff for high stomach acid when it is usually low. We are prescribed BP meds for pre-hypertension and drugs for pre-diabetes, both of which are arguably fake diseases. We have our cholesterol lowered even though it is a vital raw ingredient for making all sorts of essential hormones. And doctors think nutrition is something that weirdos and snake oil salesman care about.

I don't see my doctor about my thyroid any more, I test and treat myself. I was first told my thyroid was borderline underactive in about 1990, and I got my first prescription for 25mcg Levo in 2013. I'm not volunteering to be the first guinea pig who goes to see a doctor with hypothyroidism and a low TSH because I've done my testing when it is "sensible". I'd be thrown out with a flea in my ear.

And I wouldn't suggest anyone on here be a guinea pig either. You never know when they might change their minds about wanting to show results to a doctor. So going for the "best" results is, in my view, the sensible choice.

greygoose in reply to humanbean

Well said, HB.

@jimh111, sorry, but you live in a fantasy world. The rest of us have to live in the real world, where doctors know nothing about hormones, and care even less, and just want to brand us as hysterical women and put us on anti Ds. And some of your 'advice', could actually be damaging for the people that read it. I realise you know your stuff, as far as the chemistry goes, but, unfortunately, doctors don't. We have to put it into simple terms for them to understand. So, there's no point in theorising, we have to get our TSH as high as possible, and we do whatever it takes to that end.

Having said that, I dispute that we're 'fiddling' the results. How do you work that out? Having your test early in the morning is not fiddling. Here in France, the laboratory won't even take blood after 10.30 am. In hospital, they come round at 7.0 am. They don't consider they're 'fiddling' the results. Why is it any different when we do it?

Doctors are never going to accept that you can be hypo with a low TSH. Look how difficult it is to get diagnosed with central hypo. You had the good luck to be diagnosed by Dr Skinner. No-one is ever going to be that lucky again. And, even when he was alive, not everybody could get to see him. The majority of us have to put up with bog-standard, disinterested GPs. Please bear that in mind and, as HB said, have a little understanding and compassion for those not as lucky as you.

silverfox7 in reply to jimh111

You could get a high spike though if you take your meds as usual. I would always recommend fasting.

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