Blood test timing

[Tanyaking]

When taking NDT am I right to NOT take it 24 hours before my blood test? I've always done this, but isn't my t3 then obviously going to be low if I've not had any for 24 hours due to t3s short half life?

[greygoose]

Yes, it is. 12 hours is better, because your FT4 is going to be low, anyway, and the most important number is the FT3.

[NatChap in reply to greygoose]

12 hours would be difficult though wouldn't it if we usually take it all first thing in the morning? Sorry to jump in, just that I am going to be doing my test in a week and want it as accurate as poss!!

[jimh111 in reply to NatChap]

Suggest you divide the dose and take half at breakfast and half near bedtime. This will even out your dose and make it easy to have blood drawn during the day.

[Tanyaking in reply to greygoose]

Why will the t4 be low?

[greygoose in reply to Tanyaking]

Because of the T3 in NDT. When you take T3, the body only keeps the T4 it needs, and it doesn't need as much.

[shaws Administrator]

I leave 24 hours between T3 and test and take afterwards. Also tests were only introduced along with levothyroxine (T4), so if we take T3 or NDT, the results wont correlate so it is how we feel on a particular dose which is the best way, I believe.

web.archive.org/web/2010103...

i.e. T3 - we often hear T3 has a short half-life. It is absorbed quickly and into our receptor cells, once there it's work begins and it sends out 'waves' which last between one to three days. I'll give you a link which explains it in a bit more detail. I take T3 only - I have missed one day and felt no difference. The reason why I missed one day was I took T3 before a test and doctor, when I went into the surgery, was agitated with my result but before he said anything I said 'don't worry I took T3 before my test'. He then allowed me to have another blood test and that's when I missed one day 'so it was in my favour' and I've had no problems since.

web.archive.org/web/2010103...

[Stourie in reply to shaws]

I do the same and leave 24 hours from taking my t3 and the blood test but was told that I was wrong and should only be 12. I still leave 24.

Jo xx

[shaws Administrator in reply to Stourie]

I take it first thing, and if I a test around 12 hours later, I'd be having a blood test around 4 p.m. in the afternoon. The timing suits me perfectly and results are good.

[Stourie in reply to shaws]

I remember a few years ago I took a half dose of 40 lio the night before and my t3 was actually 15. something and was surprised that the doctor said nothing. I take my 80mcg of lio at bedtime and just leave that one out when I'm getting bloods done and the result is just under top of the range.

Just a thought, you know how tsh is lowest early on and raises during the day would it not be better for t3 users to get their bloods done as late as possible.

Jo xx

[shaws Administrator in reply to Stourie]

I'm not quite sure how that would work out. I'm happy with dose at present as am well and wouldn't like to rock the boat.

[humanbean in reply to Stourie]

TSH is highest early on in the day. It is at its lowest during the afternoon. See the graphs on page 2 of this paper :

reboundhealth.com/cms/image...

It is so that people get a TSH which is the highest possible that we always recommend to hypothyroid people that they get tested first thing in the morning.

[Stourie in reply to humanbean]

Of course, I do know that but get it the wrong way round in my head sometimes. lol

Jo xx

[Montheone]

I am having a test for T4 and hopefully T3 on thursday at 10am - was not intending to take my thyroxin on Wednesday - is this right?

[SeasideSusie Remembering in reply to Montheone]

What time do you normally take your Levo? You should leave Levo off for 24 hours before the blood draw. So if you take your Levo in the morning then take Wednesday's dose, just don't take Thursday's before the blood draw, take it afterwards.