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T4 & TSH fasting or not?
I am going monday to get my first T4 and TSH since my TT in January. I am on Synthroid 150 once in the AM. Shoud I fast before this blood draw? I want to do it right....
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213044 tn?1236531060
I've read varying opinions on the subject.

The doctors I ask don't care one way or the other.

kitty, who works in a lab, feels it makes a difference.

You could get your blood drawn fairly early (I can get it done at eight in the morning) and then take your meds.

I take my Synthroid at six, and get my blood draws about ten in the morning, consistantly. I tell myself consistantly is good, but kitty may disagree with me on the subject, and I would defer to her opinion.

I would like to see her input on the subject, again.
With all the medical jargon, like the last time. :^)
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314892 tn?1264627503
Ar- Thanks for the vote of confidence!

It is not fasting itself that is the issue. It is whether it is a good idea to take meds prior ti the blood draw.
Taking t4 containging meds before a blood draw will raise the free t4 by about 20% for several hours after swallowing the pill. This is due to a surge of t4 being released from the med. This will not affect TSH or free t3, only the free t4 result. This could result in a free t4 looking higher than it really is and make cause a doctor to think your levels are ok.
So I would do as AR said. Fast and have the blood drawn early in the morning so you can take the med immediately after the blood draw.
Consistency is very important.
TSH keveks are also at their highest in the morning and some cases of mild hypo can be missed if the blood is drawn later in the day when levels begin to drop. TSH is at the very lowest around midnight.
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213044 tn?1236531060
Nice spelling, kitty LOL!!!!
Glad to see I'm not the only one. :)

Ok, that all makes sense and maybe I can remember it this time.

Just to drag this off topic, now that the question is answered, I'll ask another.

Why do you think Synthroid is adminstered once a day?
Wouldn't twice a day give a more even distribution of hormones?
Suppose it's a compliance issue? Once a day is easier than four times a day?
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314892 tn?1264627503
I just noticed my spelling/keyboard errors!!
Can we get spell check?
I wrote this post once and lost it. Then I quickly posted it again and didn't double check it. Yikes!! Make sure to get those "keveks" checked!

T4 meds (ie, Synthroid, Lexoxy) have a very long half life (6-7 days) and are sometimes administered once per week in non-compliant patients.
It takes about 1 week for the med to build up to a consistant level in your blood, so todays dose isn't actually working today, but in a few days time.
The surge of t4 released upon ingestion only effects the blood work and is not immediately converted by the tissues into t3. T3 is the more biochemically active form of the hormone.
T3 meds have a very short half life ~ less than 1 day~ so the dose is usually split into 2 doses per day.
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213044 tn?1236531060
Thanks for the explanation! Once a day works for me, as long as it doesn't cause variations in the overall med level.

I think we may get spell check one of these days. That would be a blessing for me. Just had to rib you a little. :^)

I had to look at my keyboard to figure out what keveks were. LOL! Done that a few thousand times myself. :)
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314892 tn?1264627503
Haven't you ever heard of Keveks?
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377600 tn?1225167036
Don't feel bad, after I fussed at AR for misspelling germane--my spelling has been horrible.

I guess its Karma:)

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377600 tn?1225167036
A bit of southern history:

President Andrew Jackson stated "It's a dam* poor mind that can only think of one way to spell a word."
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314892 tn?1264627503
Thanks.
I never learned to type properly in school.
I need to proofread my writing better. Asking for spell check really is a cop-out.
What are our kids going to do if they always have spell check?
Even with mis-spellings, we can usually figure out what the other person is saying. An e-mail just went around that if the beginning and ending letters in a word are correct, our brains automatically correct for the wrong letters.
The wonders of the human mind-aahhh!
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I am taking Cytomel and Synthroid and will soon have a TSH and T4 bloodtest. Does it matter if I take my pills in the morning before the blood test? I saw the response when it just involved Synthroid, and I wondered if taking Cytomel affected your opinion. Thx.
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314892 tn?1264627503
It certainly won't effect the TSH.

Since Cytomel is T3, it shouldn't effect the t4 level either.

But since you are on Cytomel, is the doctor also monitoring your free t3 level? In that case, since t3 has such a short half life, it is best to wait to take it until after the blood draw.

I hope that is a free t4, not a total t4 you are having done. Free t4 is more accurate.
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