Bloods in the morning

[wowserclo]

Hi, I was hoping for some advice re my bloods tomorrow. I take my Levo at night and was wondering if I don't take it tonight before bloods is it ok to miss a day and take it tomorrow night? Or should I take it this eve? I don't want to double up by taking it after my bloods in the morning as that doesn't agree with me :/ thanks in advance

[jimh111]

I would take it tonight, you will get a more accurate result. Otherwise you can double up tomorrow.

[wowserclo in reply to jimh111]

Do you mean wouldn't ? Thanks

[jimh111 in reply to wowserclo]

Preferably take it tonight. If you don't want to you can take two doses tomorrow night.

[wowserclo in reply to jimh111]

I've read I'm meant to not take it 24 hours before my bloods... can't double up as that makes me feel bad

[jimh111 in reply to wowserclo]

Not taking it for 24 hours is nonsense, an attempt to get a slightly higher TSH. As long as you leave about three hours between taking the tablet and taking the blood there is no problem. I would take it tonight, you get a more accurate result and there's no worries.

[humanbean in reply to jimh111]

Only three hours? I often wonder whose interests are being served by your posts, jimh111, because I really don't believe it is the patients. Are you trying to get doses reduced to save the NHS money?

[greygoose in reply to jimh111]

No jim, it's not an attempt to get a higher TSH, we know that the TSH doesn't move that fast. But, it is going to have an effect on the FT4, if that is tested - not that doctors ever look at that, anyway.

wowserclo , does your doctor test the FT4? Even so, I doubt taking it the night before will really hurt, but perhaps take it a little earlier than usual?

[jimh111 in reply to jimh111]

On reflection I would suggest leaving at least four hours between taking levothyroxine and having the blood taken. Levothyroxine is absorbed over the first three hours and you need a little time for it to settle down. Ideally you would leave 10 to 12 hours to get the most accurate result. So for wowserclo taking the levothyroxine at night and having the blood taken the following day is ideal.

If you skip the previous night's levothyroxine dose there will be about 36 hours between dose and blood draw. This will give a falsely low fT4 figure, which you could correct by adding about 10%. However, it will be impossible to work out the real fT3 and TSH figures. The TSH will have increased and possibly had an effect on T4 to T3 conversion.

greygoose - endos are always telling us TSH does not respond quickly and they use this 'fact' as an excuse to accuse patients of not taking their medication if they find an inconsistency between TSH and fT4. TSH responds rapidly to fT3 and fT4 levels, it is the long half-life of T4 than leads to slow changes in TSH. An additional 24 hours between dose and blood draw will lower fT4 by about 10% and so increase TSH. It always amazes me that endos will tell you it takes ages for TSH to respond and then they will carry out a TSH stimulation test over a couple of hours!

It's important to try and get accurate results from blood tests. If, for example, your fT4 is around 20 but a delayed blood draw reports a figure of 18 the doctor may prescribe a levothyroxine increase leading to production of reverse T3 instead of considering an L-T3 prescription. It is very useful to keep copies of old blood test results. When new discoveries are made it may be helpful to know what your historical levels were, you need accurate results.

[SeasideSusie Remembering]

It depends on what you want your results to look like.

If you want as high as possible TSH in order to avoid a reduction in dose or to obtain an increase, then fasting overnight and an early blood draw are the best way to do that. TSH is highest early in the morning and lowers throughout the day and after eating.

[Muffy]

Don't double up on your thyroxine just because you miss one day. It has a long enough half-life to still be working in your system.