Do I need to fast for Thyroid blood test?

[Allen-P]

Hi - I need to take my thyroid test in a couple of weeks. Do I need to fast before taking the test? I take NDT (2.5 grains divided as 1.5 in morning and 1.0 in the early afternoon).

I read that I should take the test 8-12 hours after taking my dose so I was planning to switch to taking all 2.5 grains in the morning and then taking my test 9 hours later in the afternoon. No fasting.

Does that seem ok?

Thanks in advance for any help...

-a

[radd]

Allen-P,

There’s been recent discussion on the forum regarding dosing meds and timings prior to a thyroid hormone test. 

The exact origin of the forums advice in these later years appears unknown but to have been worked out from the time of assimilation and considering the hormones half life’s and particularly the peaks and troughs of T3, so works well for synthetic meds.

However, NDT works slightly differently. The intact thyroid produces T4 and T3 tightly bound to a protein called thyroglobulin, that is only degraded by a gland-linked enzyme that releases the hormones.

When we swallow NDT, the enzyme specific is missing and our hormones will remain bound to thyroglobulin until reaching the stomach and small intestine where digestion eventually releases the hormones. There is also a possible further delay in the release because the stomach enzymes are not the same as the thyroid glands, and so the two actions form a kind of natural time-release.

This delay is most likely accountable for the smoother ride many of us feel when medicating NDT. It also means testing 24 hours after previous med dose and not messing about splitting doses the day before (unless usually done) still gives an average reading, and makes life a lot easier. 

With regard to fasting before a test, yes, always.

On a slightly separate note - have you tried taking your NDT once a day? I had to split-dose synthetics, and after my switch to NDT, carried on for the last five years. Recently I switched NDT dose to once a day and feel no difference.

Both by diogenes -

How the T4 and T3 bound on to thyroglobulin are released as free hormones -

healthunlocked.com/thyroidu...

T4 and T3 in NDT are largely strongly bound on to thyroglobulin protein -

healthunlocked.com/thyroidu...

[Delgor in reply to radd]

As this question comes up a lot could it possibly be pinned.

[radd in reply to Delgor]

I'll create another post better suited to answering this subject.

[Allen-P in reply to radd]

Thank God - really great feedback. I was having a lot of trouble finding answers to this. I was thinking about skipping the split bc it's so hard to have an empty stomach in the afternoon.

So I'll take my full dose the morning before and the following morning (before eating) will get my test.

Thanks so much!

-a

[SlowDragon Administrator]

TSH is highest early morning

If your Dr is TSH obsessed then test early morning

Though on NDT it’s likely TSH is low or suppressed anyway

[Allen-P in reply to SlowDragon]

You got it. My TSH is def suppressed. Thanks...

[tattybogle]

The evidence that eating breakfast lowered TSH used to be pretty poor .....

but recently there is much better evidence that having breakfast genuinely does lower TSH .. so to show highest TSH level , an early a.m. blood test, before having breakfast is a good idea.

TSH is always lowest in the afternoon (between aprox 1-3pm) due to circadian rhythm ~ so it' a bit counterproductive fasting and having an afternoon blood test.

see the 4th reply to this post for the recent study showing effect of breakfast on TSH : healthunlocked.com/thyroidu... -list-of-references-recommending-gps-keep-tsh-lower-

[Allen-P in reply to tattybogle]

Thanks my TSH is very low, but most of the NDT feedback I get is to focus on the Free T3. But I will have the test in the morning, before breakfast. Actually I am interested to see what the TSH is with my next test (it went up a little last time). Thanks!

[helvella Administrator Thyroid UK]

Have a look at my blog post:

helvella - Factors that interfere with thyroid tests

A summary of factors known to interfere with thyroid tests.

helvella.blogspot.com/p/hel...

[Allen-P in reply to helvella]

A very interesting list. I'll have to be careful about aspirin. What about Ibuprofen and Acetaminophen?

[helvella Administrator Thyroid UK in reply to Allen-P]

Sorry - but I cannot clear them because I don't have definitive information. But as they are very common medicines (even if we call acetaminophen by the name paracetamol ), I'd have expected a strong effect to have been reported. Therefore probably no more than a weak effect, at most.