Biotin in RT3 testing

[hjh88]

Hello all,

I’ve made a bit of an oversight and realised I’ve not stopped my B complex a week before an RT3 test! I took my last on Thursday morning and will have my blood drawn at Tuesday lunchtime.

So first question I suppose is does an RT3 only assay use biotin in the process? And if so, is 5 days off biotin enough time that the test won’t be affected?

Any thoughts very much appreciated!

[SeasideSusie Remembering]

hjh88

So first question I suppose is does an RT3 only assay use biotin in the process?

Only the lab can tell you that. Some equipment uses biotin in the testing process which causes the problem of false results, most labs do but only the lab can tell you for sure.

And if so, is 5 days off biotin enough time that the test won’t be affected?

The usual amount in a B Complex is around 400mcg and it's the mega amounts, such as 5,000mcg in a stand alone biotin supplement or hair/nail supplement that needs the longer time. 3 days is probably enough for other tests.

However, an rT3 test can only tell you if your rT3 is high, it can't tell you why. There are many, many reasons for high rT3 and only one of them is to do with the thyroid and that is when there is an excess of unconverted T4 and testing FT4 and FT3 at the same time will tell you that as it will show as a high FT4 and low FT3. Testing rT3 really is a waste of time and money, frequently mentioned here.

[hjh88 in reply to SeasideSusie]

Thanks so much for this! I’ve had a slightly cryptic reply back from the lab but I take Thorne Basic B so only 400mcg as you suggest. Hoping that means a good 5 days will be alright!

And yes thought it a bit strange to test RT3 in isolation. It’s at the request of a new private doctor I’m seeing. Recommended here in fact! My FT4 and FT3 results are and have been at a decent ratio for quite some time so I think the rationale is to rule out some other complicating factors. Also testing female hormones separately in that vein too. I guess we’ll see what she says when the results are back 😂

Thanks again though for this!

[radd in reply to hjh88]

hjh88,

People often don't like RT3 results because they can be difficult to interpret but are actually only irrelevant when either viewed in total isolation, or when T4 levels are too high for that individual (as an elevated RT3 level would be expected anyway).

Reading the RT3 result in conjunction with other tests results (such as female sex hormones in your case) can make it a useful tool in confirming a reason why thyroid hormones are not working effectively in spite of good levels.

It can also give possible reasoning why 'frees' refuse to raise or why an adequate FT3 level suited to one person isn't achieving well-being for another, This is due to a proportion being converted to an inactive T3 metabolite driven by the same upregulated enzyme responsible for the RT3.

I know we usually suggest about a week but I think 5 days should be fine for the biotin to wash out as I have seen recommendations for less time before.

[hjh88 in reply to radd]

That sounds sensible and in line with what the doctor has suggested. She’s looking at ruling out oestrogen dominance and PCOS I believe so hopefully useful in that context.

That’s great though, I think between Susie’s advice about amounts and your info around timings it sounds like it’ll be ok! Appreciate it thank you.