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Thyroid UK
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Blood tests and timing of Levothyroxine

Can anyone provide me with definitive information that I can give my son's Carers about not having his Levo before he has a blood test for TSH, FT4, FT3 and HbA1c and others. For about the past 20 years he has never had his Levo before an early morning fasting blood test with the tablet being given directly afterwards, followed by breakfast after 1/2 an hour. I think there are a couple of doctors at our surgery who do not know much about thyroid meds (or anything else for that matter) and I would also like to have something official to show them, telling the reasons why.

1 Reply


There isn't anything 'official' to show them. The reason to take Levothyroxine after a blood draw is so that normal circulating FT4 is measured not the peak T4 caused by ingesting the Levothyroxine before the test. As your son's blood tests have always been done this way for 20 years for comparison purposes they should continue.


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