Blood test Protocol

[Sishey1]

Can someone please tell me the best way to prepare for a thyroid blood test - I know it involves fasting - but I can't seem to find the thread for it.

Many thanks!

[SeasideSusie Remembering]

When doing thyroid tests, we advise:

* Book the first appointment of the morning, or with private tests at home no later than 9am. This is because TSH is highest early morning and lowers throughout the day. If we are looking for a diagnosis of hypothyroidism, or looking for an increase in dose or to avoid a reduction then we need TSH to be as high as possible.

* Fast overnight - have your evening meal/supper as normal the night before but delay breakfast on the day of the test and drink water only until after the blood draw. Eating may lower TSH, caffeine containing drinks affect TSH.

* If taking thyroid hormone replacement, last dose of Levo should be 24 hours before blood draw, if taking NDT or T3 then last dose should be 8-12 hours before blood draw. Adjust timing the day before if necessary. This avoids measuring hormone levels at their peak after ingestion of hormone replacement. Take your thyroid meds after the blood draw. Taking your dose too close to the blood draw will give false high results, leaving any longer gap will give false low results.

* If you take Biotin or a B Complex containing Biotin (B7), leave this off for 7 days before any blood test. This is because if Biotin is used in the testing procedure it will give false results (Medichecks definitely use Biotin, they have confirmed this and the amount of time to leave the supplement off).

These are patient to patient tips which we don't discuss with doctors or phlebotomists.

[Sishey1 in reply to SeasideSusie]

Great! Thank you so much 😊

[Denise29w in reply to SeasideSusie]

Does this apply if you have no thyroid at all or should you take the levo so they can get an accurate reading for dosage adjustment?

[SeasideSusie Remembering in reply to Denise29w]

As far as I know it's the same. If taking Levo when you still have a thyroid, it's because your thyroid isn't producing any or enough hormone naturally, so I can't see there being any difference. At the end of the day it's how you feel on the replacement dose and it's the FT4 and FT3 that the doctor should be looking at.

[Denise29w in reply to SeasideSusie]

Thank you

[13579-2468]

Am I stupid or what. If you take medication or supplements and you stop taking before a blood test then it stands to reason that you are giving false information in the blood test. Surely what you take everyday constitutes to what your results should show. By avoiding medication before a blood test gives the wrong figures. you are in effect manipulating the outcomd

[SeasideSusie Remembering in reply to 13579-2468]

If you read the advice again you will see the explanations.

If someone has symptoms and is looking for a diagnosis of hypothyroidism, then TSH needs to be as high as possible because most GPs wait until it reaches 10 before diagnosing. Therefore an early morning, fasting blood draw is the best option.

As for the time gap between last dose of Levo and blood draw, as FT4 peaks 2-4 hours after ingestion of Levo then that gives a false high result. Same with T3 and FT3 result. That can lead to a GP reducing a dose when the patient is probably on their correct dose.

Leaving too long after taking Levo or T3 before blood draw can give false low results and may lead to a GP increasing dose and causing overmedication.

So taking thyroid hormone replacement after the blood draw is best (assuming the patient normally takes it in the morning) and is actually recommended. I'm on my tablet and can't do links to PDFs so will go to my PC and come back and edit to add the link.

Edited to add link:

sps.nhs.uk/wp-content/uploa...

This link has been provided by Admin team member SlowDragon and is for the NHS Specialist Pharmacy Service, it says on page 13 under "Primary Care Monitoring"

Monitoring is by TSH levels measured from blood tests taken prior to the morning medication.

Although monitoring by TSH alone is not a good indicator of thyroid status, it clearly states to not take hormone replacement before the blood draw.

[13579-2468 in reply to SeasideSusie]

Thank you for explaing that