Blood Test

[Boney12]

Hi I have a blood test at 11am tomorrow morning should I take my levothyroxine before I go? I usually take it around 8am on an empty stomach.Thankyou

[Jaydee1507 Administrator]

It's recommended to get blood tests done at 9am or as close as posssible as this is when TSH is at its highest. Can you rebook the blood test? GPs dose us on TSH and you will get a lower dose as a result of testing later.

On day before test, take Levo so it will be 24hrs until the blood test next day. On day of test take Levo after test.

TSH graph

[tattybogle]

if you go to this post, healthunlocked.com/thyroidu...

and look in the replies you will find links to a study which explain why it is best practice to test TSH in the early am (around 9 am ~ when it is higher than at 11am )...and before taking that days dose of Levothyroxine .( because taking Levo too close to fT4 test affects the fT4 result and does not give true picture of the average level over the day , you get a false high fT4 result between approx 2 to 6 hours after taking the tablet when the fT4 level peaks very sharply as the full dose is absorbed into the bloodstream all at once ) The fT4 level than falls slowly after that , so for consistency it is best to always leave a 24 hour gap after last dose of Levo for an fT4 test.

Also a link to a study showing why it is best to not have breakfast before taking the TSH blood test . Eating breakfast lowers the TSH . .. and eating different things for different blood tests may have greater or lesser effects. .. so for consistancy it is best to always wait till after the test to have breakfast (another reason to get the test done as early as possible )

You dose is decided based on TSH by most GP's.. if it is lower than they like to see ,your dose may be reduced inappropriately. (or if you need a dose increase it may not be given if TSH is not seen as high enough )

And the fT4 result may look too high if tested shortly after taking the days dose.. which may also result in the GP inappropriately decreasing your dose.