Doing a thyroid screen tomorrow- what do I do about my morning dose of levo? And should I fast for 8 hours?

[Indiana12]

Thyroid screen

Home finger prick test

[greygoose]

You' mean a blood test? Take your levo after the blood draw, otherwise you'll have a false FT4 level.

Best to fast over-night, yes. Just drink water.

[SeasideSusie Remembering]

Drink water only before doing the test, caffeine containing drinks and some foods can affect TSH.

Last dose of Levo should be 24 hours before the test.

[SlowDragon Administrator]

What vitamin supplements are you currently taking

Remember to stop taking any supplements that contain biotin 5-7 days before any blood tests

[Indiana12 in reply to SlowDragon]

Thank you. What is biotin usually found in?

[SeasideSusie Remembering in reply to Indiana12]

B Complex, also hair and nail supplements.

[jimh111]

Taking the levothyroxine before the blood test will give an fT4 result that is very slightly high. Fasting makes no difference although it is commonly believed to do so because of one sloppy study that received extensive publicity.

[SeasideSusie Remembering]

From Thriva website (who do thyroid testing)

thriva.co/hub/thyroid/how-t...

Things that can affect your thyroid function results

Fasting

Generally, you don’t need to fast before doing a thyroid function test. However, not fasting is sometimes linked to a lower TSH level. This means your results might not pick up on mild (subclinical) hypothyroidism — where your TSH levels are only mildly elevated.

So it depends on whether your TSH result is important so bear in mind that not fasting can produce a lower TSH.

[jimh111 in reply to SeasideSusie]

Thrive do not do thyroid (or any other) testing as far as I can see. They are agents who market tests, a bit like a travel agent probably can’t pilot an airliner. The author of this document has a nutritional science degree and works as a “content designer” with no thyroid knowledge as far as I can determine.

I’ve written to Thriva asking for evidence as I suspect they just cobbled together some notes after consulting Dr Google. If I get a reply I’ll summarise it here and can pass it onto anyone who wants a full copy.

[SeasideSusie Remembering in reply to jimh111]

My post wasn't addressed to you.

[jimh111]

Thriva have reviewed their advice and removed the comment that begins "Generally, you don’t need to fast before doing a thyroid function test" and have added some comments about the time of day affecting TSH.