Accurate Blood Test Results (thyroid)

Hi lovelies.

Will be going to get my monthly bloods done on Saturday and was wondering if you have any tips on how to get a more accurate result.

Should I not take my meds till after the test? Should I fast?

I have been feeling very fatigued lately so if it is related to thyroid I obviously want my levels to be low enough to actually get the doctors attention. I will also be getting my iron levels checked, would fasting affect this?

Thank you!

17 Replies

I have exact same questions my friend! Anxiously awaiting some feedback I am due for testing in two days 😯 xx

Get the blood test as early as possible, don't take meds before. I don't eat before mine simply because I like to take my medication first but I don't think that you need to fast for thyroid. You shouldn't eat anything for 8 hours before and iron test.

Is it okay if I were to eat? Would it make such a massive difference? It says no fasting but I think I will need to eat before as won't get there till 9:30.

Possibly with iron.... that's what I've read any way... I guess it makes sense as it's something you get from food but mines a little on the high side anyway as is common for people from Celtic/Gaelic backgrounds so it's not something I check much anyway. Can't you bring something to eat after?

It's really a case of like for like, some clinic suggest to do the same for each blood draw.

Im taking T3 only so I always fast for 12hrs, no meds and drink only water. Test as near to 8am as possible.

For iron panel and B12.... I stop B12 and iron supplements 5 days before the test.

I'm told Potassium and calcium can be falsely elevated if a tourniquet is used at the blood draw, you could ask them not to use one.

Yes, get your test first thing in the morning and don't take thyroid meds for 24 hours (Levothyroxine or NDT) or 12 hours (T3). Those are the most important. Fasting is said to make a difference, in particular drinking anything containing caffeine is said to lower TSH, which you don't want. I don't think fasting affects iron levels - it's not a question I have seen asked before.

Of course if you want your levels to be "low enough to actually get the doctors attention" you could leave off the Thyroxine for a few days before the test, but that wouldn't necessarily reflect your thyroid status (although I'm not saying I haven't done that myself!).

Thank you! I am not too sure if I should stop the meds. Because, if the fatigue isn't from my thyroid I don't want them to assume it's just thyroid-related. But last time I went in for fatigue she suggested a teen phycologist.... they want to diagnose you with anything but..

GPs are paid extra to treat mental illness, so they just love to diagnose depression and other conditions.

Is it okay if I were to eat? Would it make such a massive difference? It says no fasting but I think I will need to eat before as won't get there till 9:30.

I think steering free of drinks containing caffeine is the most important thing. Food does make a slight difference but having the test first thing in the morning, and not taking any thyroid meds for 24 hours beforehand make the biggest difference as I understand it.

hollygrace99 The advice always given on the forum for testing thyroid, when TSH is important to be high in order to avoid a reduction in dose of Levo or when looking for an increase is:

1) Book the earliest appointment of the morning. TSH is highest early morning and lowers during the day.

2) Fast overnight (water allowed). Eating lowers TSH.

Also, when the free T results are important:

3) Leave off Levo for 24 hours - take it too close to blood draw and you'll get a result reflecting that you've recently taken it due to when it peaks in the blood. -

"...... Time-course analysis showed that free and total thyroxine levels remained significantly elevated above baseline for 9 and 5 h, respectively, after a levothyroxine dose. In conclusion, there is a transient increase in thyroid hormone levels for 9 h after an oral levothyroxine dose. Accurate assessment of thyroid hormone levels in patients receiving levothyroxine therapy should take this into account. ....."

4) Any T3 meds - T3 or NDT (because it contains T3) - leave off for 12 hours. Again, taking it close to blood draw shows you've recently taken it and will give a high result. Leaving it more than 12 hours will give an artificially low result. When taking T3 in any form it's the FT3 result that is most important so if taking NDT it should be left off for 12 hours not 24.

Thank you.

Is there anything that helps to raise my TSH?

Only having the very earliest appointment of the day and fasting overnight will give the highest TSH. As I said previously, TSH is highest early morning and lowers throughout the day, and eating lowers TSH.

If you have started Levo, TSH will be lower anyway because it's a pituitary hormone that tells the thyroid to produce thyroxine if it detects that there isn't enough (Thyroid Stimulating Hormone) and if you take Levo the pituitary will detect that there is already some thyroxine and wont need to tell the thyroid to produce any.

If I am already on levo. Should I not take it tomorrow (friday) as I will have the test Saturday morning?

I just don't want to be too tired because I'm going out Friday night and have a full day. Will it cause symptoms or just change levels or none because it's just one day

You leave off Levo for 24 hours before the blood draw. So depending what time you normally take it, work it out from there.

If you take your Levo first thing in the morning, on rising, then take Friday mornings but don't take Saturday's until after the blood draw.

Leaving off a dose of Levo or delaying it wont give you any symptoms or make you tired, it's not an instant thing like taking an asprin. Levo builds up in the body, the full effect of a dose change takes about 6 weeks - and that is changing your permanent dose, not just changing one day.

Is it okay if I were to eat? Would it make such a massive difference? It says no fasting but I think I will need to eat before as won't get there till 9:30.

hollygrace99 When TSH is important - as in getting a diagnosis, when looking for an increase in Levo or to avoid a reduction, then you need TSH as high as possible. As already explained in a previous reply, eating lowers TSH. So if you need a high TSH for the reasons given, don't eat breakfast before the blood draw.

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