Blood results tsh levels

[jojojowilts43]

I've just got result back from bloods I hadn't taken last Thursday. My last result said tsh was at 2.84 but this time is at 3.7 .. anybody know why that would and is it normal for it to fluctuate? At the time of having blood test I had been on nitrofuratoin (antibiotics for 3 days only for a urine infection) could that of affected my result?

[SeasideSusie Remembering]

Were both tests done under the same conditions ie

Same time of day (hopefully first appointment of the morning)

Overnight fast

Left off Levo for 24 hours

Were you taking the antibiotic at the time of the test? Some antibiotics increase thyroid hormone absorption, some decrease it. General advice is to take antibiotics 6 hours away from Levo.

[jojojowilts43 in reply to SeasideSusie]

THis last test was just after 10am but can't remember what time the one before was.. I wasn't told to fast for the test and can't even remember if I'd taken levo before the test don't think that I did mind you.. I'd had a antibiotic the night before the test but don't think that would of affected the result? I didn't know to take it 6 hours away from levo. Jeeez I took it about an hour after I'd taken my levo .. just wondering what's made my level go up . Is it very important to take at exactly same time everyday?

[SeasideSusie Remembering in reply to jojojowilts43]

If you want to compare test results, then you need the same conditions every time. That's why it's always advised here to book the first appointment of the day for the blood draw (which is when TSH is highest and useful if looking for a diagnosis, an increase in Levo or to avoid a reduction in Levo), plus the overnight fast and to leave off Levo for 24 hours. If conditions are different each time, comparison can't be made.

So chances are that your previous TSH of 2.84 was when blood had been taken later in the day, as TSH is highest early morning and lowers throughout the day.