Prep For Thyroid Blood Test?

[B12again]

Hi folks. I’m sending off a blood test next Monday for FT3, FT4, TSH, anti-Tg, anti-TPO and want to prepare properly for taking the bloods.

I’ve taken in doing it before 9am, drink only water. But unsure about vits, I’m taking Fish Oil, magnesium, B Complex, D3+K. I also SI B12. I think I heard one should stop the B Complex 72hrs before because of B6.

Some confirmation, addition or amendment would be very welcome. Thank you. 🙂🇬🇧

[SlowDragon Administrator]

Yes stop Vitamin B complex 3-5 days before testing (because of biotin)

In days before blood test, when you stop vitamin B complex, you might want to consider taking a separate folate supplement (eg Jarrow methyl folate 400mcg) and continue your SI B12

Recommended that all thyroid blood tests early morning, ideally just before 9am, only drink water between waking and test and last dose levothyroxine 24 hours before test

This gives highest TSH, lowest FT4 and most consistent results. (Patient to patient tip)

Looking at previous posts

You only increased dose 4 weeks ago?

Test 6-8 weeks after any dose change or brand change in levothyroxine

[B12again in reply to SlowDragon]

Thank you, very helpful. If I remember, the only post I made about increasing dosage was to ask about thoughts on me raising it myself by splitting tablets. The consensus seemed to indicate caution. I’ve been on 50 micrograms for a number of years. I did have a TSH (3.2) test done at my surgery a couple of months ago but would not do them all. 😤

[SlowDragon Administrator in reply to B12again]

Ok ….so not increased dose yet

Get full testing…..likely to show under medicated

TSH should be under 2 as an absolute maximum when on levothyroxine

gponline.com/endocrinology-...

Graph showing median TSH in healthy population is 1-1.5

web.archive.org/web/2004060...

Comprehensive list of references for needing LOW TSH on levothyroxine

healthunlocked.com/thyroidu....

onlinelibrary.wiley.com/doi...

If symptoms of hypothyroidism persist despite normalisation of TSH, the dose of levothyroxine can be titrated further to place the TSH in the lower part of the reference range or even slightly below (i.e., TSH: 0.1–2.0 mU/L), but avoiding TSH < 0.1 mU/L. Use of alternate day dosing of different levothyroxine strengths may be needed to achieve this (e.g., 100 mcg for 4 days; 125 mcg for 3 days weekly).

Guidelines of dose Levo by weight

approx how much do you weigh in kilo

Even if we frequently start on only 50mcg, most people need to increase levothyroxine dose slowly upwards in 25mcg steps (retesting 6-8 weeks after each increase) until eventually on, or near full replacement dose

pathlabs.rlbuht.nhs.uk/tft_...

Guiding Treatment with Thyroxine:

In the majority of patients 50-100 μg thyroxine can be used as the starting dose. Alterations in dose are achieved by using 25-50 μg increments and adequacy of the new dose can be confirmed by repeat measurement of TSH after 2-3 months.

The majority of patients will be clinically euthyroid with a ‘normal’ TSH and having thyroxine replacement in the range 75-150 μg/day (1.6ug/Kg on average).

The recommended approach is to titrate thyroxine therapy against the TSH concentration whilst assessing clinical well-being. The target is a serum TSH within the reference range.

……The primary target of thyroxine replacement therapy is to make the patient feel well and to achieve a serum TSH that is within the reference range. The corresponding FT4 will be within or slightly above its reference range.

The minimum period to achieve stable concentrations after a change in dose of thyroxine is two months and thyroid function tests should not normally be requested before this period has elapsed.

[B12again]

Thanks Slowdragon, informative and very helpful.