Blood test timing

[Pinkpetite]

Hello everyone. My daughter has 2 options for a blood test - 1pm or 7.40pm - we can't wait for a morning slot as she needs it done before her appt.

She has M.E. so gets up around lunchtime anyway so would 1pm be best as she can then just have water and no food?

Would this still give the highest TSH reading even though it's 1pm?

Thank you 🙂

[SeasideSusie Remembering]

PinkPetite

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Would this still give the highest TSH reading even though it's 1pm?

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It depends on whether the GP is dosing purely by TSH and she's looking to avoid a reduction or achieve an increase in her dose of Levo and needs the highest possible TSH.

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The first graph in the following post shows the fluctuations in TSh during the day. A blood draw at 1pm would give a slightly lower TSH than one at 7.40pm but both still very much lower than a 9am blood draw.

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healthunlocked.com/thyroidu...

[Pinkpetite in reply to SeasideSusie]

Ok so I may as well go for the 7.40pm - better of the 2 options atm?

[SeasideSusie Remembering in reply to Pinkpetite]

Pinkpetite

Very slightly better but that graph shows a difference of what looks to be around 0.1-0.2ish.

Then there is fasting, if she has the 7.40pm appointment, how long can she fast for?

It might not be worth it having the later appointment for such a small difference.

[Pinkpetite in reply to SeasideSusie]

No she can't fast all day. Can I ask what the fasting does? How it affects the results?

If she ate at 2pm for the 7.40pm test would that help?

[SeasideSusie Remembering in reply to Pinkpetite]

Pinkpetite

Eating can lower TSH. Also, water only before blood draw, coffee can affect TSH.

[Pinkpetite in reply to SeasideSusie]

Ok best to fast then.

Thanks 🙂

[SlowDragon Administrator]

Previous post shows dire ferritin, low folate

High thyroid antibodies

What vitamin supplements is she taking?

Iron supplements should be stopped a week before testing iron levels

Last dose of Levothyroxine 24 hours prior to blood test. (taking delayed dose immediately after blood draw).

This gives highest TSH, lowest FT4 and most consistent results. (Patient to patient tip, best not mentioned to GP or phlebotomist)

[Pinkpetite in reply to SlowDragon]

She is on iron. They are testing her serum iron and ferritin, no FBC, as well as a full thyroid panel, vit B12 and folate.

Just realised we will have to go for the 1pm slot as she took her thyroxine today at lunchtime and not tonight - for tomorrow's 7.40pm test. The 1pm slot is Saturday.