Blood test time

[Min789]

Hi, I have to book a blood test for the end of October for thyroid. Should I make it for 8am as the clocks will be going back the weekend before?

[LittleSchnau]

Hello! From a personal perspective, I try to have a similar time and same conditions (ie fasted, no medication taken) every time. Even though the clocks are changing, it shouldn’t make too much difference if you’re still aiming for an appointment early morning if available from your provider.

[Regenallotment Ambassador]

I agree with LittleSchnau , as long as its consistent for you and close to the morning window when (patient to patient tip) TSH is likely to be highest and therefore most useful for diagnosis or monitoring for increases.

Personally I take my Levo every morning at 6am and I am on the road for work at 7.30 so I do my private at home finger prick testing at 6am, GP testing is often not before 10 am as the earlier appointments are impossible to get round here. My prescriber for T3 says that from her perspective there isn't a huge amount of difference and she's monitored 000s of people over the years. I don't agree from my personal experience. But if you are looking for a diagnosis or an increase then of course, small margins matter 🙂

[Min789 in reply to Regenallotment]

I suppose my only concern is that admin tend to advise having blood test as near as possible to 9am as then TSH will be at its highest. As I have extremely low TSH I feel that I need to keep it as high as i can otherwise my GP will try to lower my dose. I feel well on the current dose and don’t want him to have an excuse. Once the clocks go back then 9am becomes 8am. If I go at 9am then that would have been 10am before clocks went back. Maybe I am worrying unnecessarily and an hour either way will make no difference to my TSH.

[Regenallotment Ambassador in reply to Min789]

Indeed, when it matters, it really matters, I hear you. I think your line of thinking is logical too, I was just trying to suggest that some hold alternate views, and some can't get appointments at the ideal times or life happens 🙂

[tattybogle]

hi Min, just go as early as you can if getting highest TSH is what matters to you.

your HPT axis has no idea we put the clocks back, we change the clocks 'overnight' , but the body's diurnal rhythm doesn't change overnight just cos someone moved the clock hands , these rhythms change very slowly based on such thing as seasonal changes in daylight hours etc etc

there is nothing magical about 9 am , some may have a slight rise around that time , some may not ~ i've never seen any evidence that convinced me TSH goes up a bit at 9 am , just one rather iffy looking graph that appears to have a small blip at that point, but if you look at it carefully it's not at all clear what was actually going on ..... all we can say with any degree of certainty is that TSH is naturally highest middle of the night /very early am.... and gets gradually lower over the morning until its lowest point around early afternoon, then gradually rises again.

in some people this diurnal difference in TSH may be enough to be significant (ie just in range vs just under range ... in others (especially if TSH is supressed/very low), there may be no difference at all.

but if 'highest possible TSH' is the name of the game, then the earlier you test, the more likely you are to get a slightly higher result.