Advice please

[shortytree]

I'm at dry again for thyroid blood test and full blood count would I get a more accurate result if I don't have breakfast

[shaws Administrator]

All blood tests for thyroid hormones should be the earliest possible and don't eat before it (you can drink water). Also leave about 24 hours between your last dose of levo and the test and take levo afterwards. This helps keep your TSH higher than it would be if it was later in the day (it drops throughout the day) and food intereferes with the uptake.

[Clutter]

Shortytree,

You'll get a higher TSH result if you test early in the morning and fast (water only) as TSH is highest early and drops after eating and drinking.  If you take Levothyroxine make sure to take it after the blood draw.

[shortytree in reply to Clutter]

Thank you shows and clutter I'm not at Dr s until 11 am so I will just have water . Fingers crossed they don't just say normal range again 

[greygoose in reply to shortytree]

Do you have to have your bloods done whilst at the doctors? Can you not make some excuse to go back another time - early in the morning - for the actual test?

[helvella Administrator]

Trouble is, there is a peak of FT4 approximately two hours after taking the tablet(s). That peak slowly fades.

If the assessment is based on that peak, because that was when the blood was drawn, you could easily see your medication being reduced when it shouldn't be.

Were the system to ask what your dose is and when you took it, and take into account that peak, possibly a sensible decision could be reached. It seems to me that is extremely unlikely in an ordinary GP appointment.

I would like to put forward as evidence details of my FT4 over the years. Rather a shame they only do TSH.

[Clutter]

CarpaBob,

T4 levels peak up to six hours after taking Levothyroxine.  To see normal circulating levels of T4 in the body Levothyroxine should be taken after the blood draw.

[CarpaBob in reply to Clutter]

Isn't the point though to see what the levothroxine is doing though. I did do some research and what I found suggested you should take as normal and have your blood test as early in the morning as possible in which case is it can be taken before your levothyroxine is taken and you get the result without skewing the results.  if you skip a morning dose and have blood taken in the afternoon say wouldn't that mean your tsh goes up to trying compensate for not taking the levothyroxine?

[Clutter in reply to CarpaBob]

CarpaBob,

Having the blood test before the Levothyroxine dose shows normal circulating levels in the blood stream.  Taking Levothyroxine before the blood test measures the peak levels of Levothyroxine in the blood stream.  Delaying Levothyroxine dose for a few hours doesn't alter TSH. You'd have to skip several doses of Levothyroxine before TSH started rising.    

TSH follows circadian rhythms and is highest at midnight and declines through the day which is why early morning and fasting tests are recommended.  See graph in the link below.

healthunlocked.com/thyroidu...

[CarpaBob in reply to Clutter]

OK, on the subject of circadian rhythms my husband works a back shift so we go to bed at 4am and get up at say 12pm.  Would you or anyone else know if my circadian rhythm would be changed at all in respect of tsh levels. I take my levothyroxine on waking at 12pm. I normally book blood tests for 8am due to the thinking that morning gives best levels but I do wonder if the fact that I have a different day pattern means I should have them taken when I normally wake. 

[Clutter in reply to CarpaBob]

CarpaBob,

Your work and wake schedule doesn't change your body's natural circadian rhythms. 

Thyroid testing is a snapshot in time of levels.  There's no best or worst level but early morning and fasting tests will show TSH at it's highest.