Blood Tests - what to take or not beforehand

[cled2wyn]

Hi, I am a little confused as I am due my 3 monthly blood test for Hyperactive Thyroid and have been told to stop medication 24 hours before the test. I am on Carbimazole 5mg alternate days (Hyperactive Thyroid) and 20mg Hydrocortisone daily (for Adrenal Insufficiency). As my Carbimazole is alternate days does it count as 24 hours without medication on the alternate day? Should I continue Hydrocortisone regardless of blood test?

[PurpleNails Administrator]

I think you need to double check with your doctor.

The blood test might not just be for thyroid function in which case they may mean your other medication too.

My doctors have never said to delay or to take Carbimazole prior to test. It doesn’t have an immediate affect so I’m not sure why it would be required.

If you take a supplement containing biotin then leave off a few days before draw. Biotin can skew results.

Did the doctor ever explain the cause of you hyper?

[cled2wyn in reply to PurpleNails]

Thank you for your prompt reply. It has never been explained to me what the cause of my hyper is. I will ask when I speak with the Endo for the results. I will double check before my blood test about stopping Carbimazole but thank you for your comments.

[pennyannie]

Hello Cled2wyn :

I've just looked back at your first post and wondered if you have now had the medical proof of which antibody has come back positive and over range ?

There 2 two thyroid auto immune diseases that start off the same way - one is actually transient ' hyper ' and the T3 and T4 levels come back down into range themselves and no medication is prescribed.

With Graves the T3 and T4 thyroid hormones keep rising and rising which is considered life threatening if not medicated and so an Anti Thyroid drug, like Carbimazole is prescribe to block your own thyroid hormone production.

Initially the only way to spot the difference is through the thyroid antibody readings and we look for a TR ab - a thyroid receptor blocking antibody and/or a TSI - a thyroid stimulating antibody for Graves.

Whilst for Hashimoto's we look for a TPO - a thyroid peroxidase and/or a TgAB - a thyroglobulin over range and positive reading :

Do you hae your original blood test at diagnosis before starting any Anti Thyroid medication and does it show a TSH, T3 and T4 result and range please ?

I'm sorry I do not know the answer to the question asked and have just given you more questions - but why not phone the doctor for advice on this blood test procedure ?

[cled2wyn in reply to pennyannie]

Thank you for your in depth reply. This is all new to me and is taking me a long time to understand enough to ask intelligent questions when taking to the endo

[pennyannie in reply to cled2wyn]

Yes I totally understand - but since you are legally entitled to copies of all your medical records and history ' just thought ' this letter containing ( the gobblegook ) and the relevant information could just sitting there waiting to be explained to you.

[helvella Administrator Thyroid UK]

The problem is that Carbimazole has a very short half-life.

It is often advised to split-dose, within a day, particularly at the start of treatment, because one dose can more-or-less run out within 12 hours - let alone 24. The half-life quoted varies a bit, but somewhere around 5 to 7 hours is often suggested.

The half-life of methimazole is 3 to 5 hours

pubmed.ncbi.nlm.nih.gov/617...

(Methimazole is extremely similar to Carbimazole - indeed, Carbimazole speedily converts to Methimazole in the body.)

Whilst it is also common for people to move to once a day dosing with experience and care, every other day seems a bit too long a gap.

This makes it very difficult to give useful advice.

[cled2wyn in reply to helvella]

Thank you for your reply. I will certainly ask about this when my blood test results are through