Interesting Comments From Lab With Test Results

[Shelley1954]

Printout of test results, 2 comments from the lab

1. "Please note: if measurement of free T3 levels is desired, a sample should be taken shortly before next dose of medication is administered. This is to ensure consistency of testing in the face of the wide variability in post dose free T3 levels." ( Of course I fasted as well as no meds, as we all know we should but this message is never passed on!

2. " New free T3 reference range reported which now encompasses 95% of a normal population. (The previous range applied to 90% of a normal population.)" This is interesting anyone else had this?

[SeasideSusie Remembering]

I've not had it, my last Blue Horizon test was a few weeks ago and no comments on that, and I always put what meds I take on the form.

I've just done another one with added reverse T3 (needs to be tested again), that might be done at a different lab so it will be interesting to see what comments are with those results.

Who was your test done with?

[jimh111]

If you draw the blood shortly after taking T3 the assay will give a silly result. If you wait until just before your next dose you will get a reading that is unrealistically low. If you are taking T3 containing medication you need to have the blood taken about half-way between two doses. Comment 1. is dangerous, particularly if more attention is paid to the blood test than signs and symptoms. This lab seems to understand biochemistry but not the risks to the patient.

[smudger1 in reply to jimh111]

Must admit I always do a blood test before taking my next dose, so for T3 approx 12 hours after last dose and T4 24 hours.

[RedApple in reply to smudger1]

That makes sense to me smudger1

[RedApple in reply to jimh111]

jimh111

If you wait until just before your next dose you will get a reading that is unrealistically low.

I disagree on that. I think it's important to know what your level is shortly before your next dose. If it's mid or high in range, then you can consider whether the next dose is in fact going to overdose you. If it's very low in range, then you know you definitely need the next dose. Either way may be a good indication that adjustment is required.

Taking the test half way between doses just leaves you wondering, in my opinion.

[jimh111 in reply to RedApple]

Thyroid hormone receptors need to be staturated in T3 for several hours before they activate. With a medication you have a saw-tooth pattern of levels, especially if the half-life is short. You want to know the average level of hormone. Ideally you should measure the area under the curve but this is not practical, so the mean is the next best option. If you take a measurement just before the next dose you don't know what your average dose is. Also the measurement before the last dose would be differ according to how frequently you took the medication. Ideally we would all be fine on levothyroxine or slow release T3 would be avialable.

It depends on whether you want an accurate result. If you're not bothered don't bother spending money on the blood test!

[Clutter in reply to jimh111]

Jimh111,

A result is simply a snapshot in time. It is always accurate. 8-12 hours after last dose will enable a reasonable estimate of normal circulating FT3.

[jimh111 in reply to Clutter]

Yes that's fine for once daily dosing, I was assuming twice daily.

[wellness1 in reply to Clutter]

In the case of someone who takes NDT one time per day upon waking, would it make sense, on the day before testing to skip the morning dose and take it at night for a next morning blood draw?

[Clutter in reply to wellness1]

Wellness1,

I wouldn't bother. Adding +20% to your FT3 result should give a reasonable estimate of your normal circulating T3.

[jimh111 in reply to wellness1]

If you take T3 once a day and the half life of the T3 is 24 hours (it may be longer) and you have no thyroid output. Then after 12 hours there would be 70% left, so this would be your average level. After 36 hours you would have 35% left. So if the blood was drawn 36 hours after the last dose you would need to double your fT3 figure.

If you take NDT then you will be getting some T3 from the T4 in NDT and it becomes a lot more complicated! I would guess at adding 50% but it might be easier to just take your morning tablet as usual and have the blood taken late afternoon.

[Saggyuk in reply to jimh111]

I normally do this actually. I take three times a day but never leave blood test much more than six/seven hours after last dose as my levels start dropping silly amounts quickly after this and tsh raises fast too and doesn't give me accurate result - for me anyway. I just leave what ever dose would normally be taken during this time a little later. Or if having early morning test, will leave the last dose of the day before until just before I go to bed and spread them out a bit more.

[wellness1 in reply to jimh111]

Thanks, jimh111 . I've made it a point to be consistent with testing, opting for early morning. This is suggested as the optimal time for purposes of TSH, but staying consistent also allows for comparing results. It's all really interesting, but I admit I'm still a tad bit confused. Maybe I'll just post next results here (making note of time of blood draw and previous dose) and kind souls such as yourself can advise.

[humanbean]

" New free T3 reference range reported which now encompasses 95% of a normal population. (The previous range applied to 90% of a normal population.)"

Two reactions :

1) Fewer of those pesky hypothyroid patients complaining about low T3?

2) Could it delay treatment for hyper patients? I don't know how often that is an issue.

[Saggyuk in reply to humanbean]

Actually, I have noticed all the labs changed for my results changed in the last year - most of them have increased the lower and upper range which is good isn't it? For hypos anyway? I think the upper range went from 6 to 6.8 on my usual lab.

Most endos in my experience advise to dose T3 frequently throughout the day rather than once so am sure the first issue means not to dose so soon after last dose as will have high levels shortly after?