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Confused about lab results/med changes

I am 26, and have been on Synthroid 75mcg for 5 years now with normal lab values. A couple weeks ago I noticed I've been more fatigued in the afternoon, with difficulty focusing, and a lot more mental fog. I went in for a thyroid check and my levels are:

TSH -  0.43   (low normal according to doc)
Free T3 -  2.60    (low normal according to doc)
Free T4 -  1.25    (slightly high according to doc)

Doctor is increasing my Synthroid to 125mcg, and wants to add a med named Armour?? Which I've never heard of. I am so confused now because having a low TSH usually means more along the lines of HypERthyroid right? I've never seen low TSH and high FT4 and don't understand why the increase in Synthroid and adding Armour. Does anyone understand those values and the medication? Please help!
Best Answer
Avatar universal
Do you have the reference ranges on your FT3 and FT4?  Ranges vary lab to lab so have to come from your own lab report.

Armour is desiccated porcine thyroid.  It contains both T3 and T4.  Synthroid only contains T4.

Once on meds, TSH often becomes totally unreliable in determining thyroid status.  Since TSH is a pituitary hormone and a very indirect measure of thyroid status, many factors can influence it.  You really have to go by FT3 and FT4.

When TSH is high, FT4 is typically low, and when TSH is low, FT4 is typically low.  TSH is counterintuitive.

Unless your lab has an unusual FT4 range, your result doesn't look high to me.  However, that's just a guess, and I have to see your lab range before commenting further on that.

My first comment on the meds change is that if your doctor thinks your FT4 is "slightly" high, he shouldn't be increasing your Synthroid.  That's going to make it even higher, and that's a pretty hefty increase.  Once again, however, your FT4 doesn't look high to me.  Your FT3 does look "low normal", and I think that's why he wants to add some Armour...to get your FT3 level up a little.  How much Armour is he adding?  

Do you understand how T3 and T4 work?  I'll be happy to explain...

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Avatar universal
Thank you! You guys helped me understand this a lot better!! I did research about Armour as well and decided this next month I get a refill I will stop Synthroid altogether and start Armour so I get more T3. Thanks again!
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Avatar universal
Well, your doctor was right; your FT4 is a little high.  That's a very low FT4 range.  I don't think I've ever seen one that topped out that low before.  

Synthroid's active ingredient is T4.  So, the 75 mcg you've been taking everyday (along with whatever your thyroid might still be able to produce) is what's making your FT4 level high.  No feedback mechanism has been identified for conversion, so we don't really know how the body determines how much to convert.  

It is odd to want to increase T4 even more when it's already over range.  Typically, increases are on the order of 12.5-25 mcg at a time.  So, I would seriously question a 50 mcg increase at this point.  I appreciate the fact that he's treating your symptoms, but I find his approach a bit too aggressive.  Did you say he was adding Armour as well?  

Yes, T4 is the "storage" form of the thyroid hormones.  It's made in the thyroid and basically floats around in your bloodstream until it's needed.  However, cells can't use T4 until it's converted to T3.  Some T3 is made in the thyroid, but the vast majority is converted at the site that needs it.    
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Avatar universal
Don't forget ferritin also.  Very important for good thyroid function.  Women need ferritin in the area of 70-80.
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Avatar universal
Thank you guys both for those explanations! I didn't realize the reference ranges vary so these are it:

TSH - 0.43 (0.34 - 4.50)
FT3 - 2.60  (2.50 - 3.90)
FT4 - 1.25 (0.54 - 1.24)

I understand now that sometimes the T4 does not convert to the active T3 in your body, hence why T3 would be low. But how come T4 is high? Does it just keep producing and producing, and not realize that it's not being converted? I'm assuming the doctor wanted to increase Synthroid based on clinical findings of me having brain fog/fatigue/lack of concentration, and not based on labs alone..but it's odd to want to increase T4 even more.

Am I correct in thinking now that T3 is the hormone that is most responsible for symptoms and thyroid function? And that T4 is just the inactive state that converts it to an active hormone?

PS - Gimel thank you for the Vit D/B12 information, I have a history of that and will get that checked!
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Avatar universal
TSH is a pituitary hormone that is supposed to accurately reflect levels of the biologically active thyroid hormones, Free T3 and Free T4.  In reality TSH cannot be shown to correlate well with either, much less correlate well with symptoms, which should be the first concern.  

The main value for TSH is in the initial diagnosis.  After starting on thyroid med it is basically useless as a test.  Scientific studies have shown that Free T3 correlates best with hypo symptoms while Free T4 and TSH do not correlate at all.   In addition, when taking thyroid med, patients frequently find that in order to raise their Free T3 and Free T4 enough to relieve symptoms, their TSH becomes suppressed below range..

A good thyroid doctor will treat a hypo patient clinically by testing and adjusting Free T3 and Free T4 as necessary to relieve symptoms, without being constrained by resultant TSH levels.  You can get some good insight into clinical treatment from this letter written by a good thyroid doctor for patients that he sometimes consults with after initial tests and evaluation.  The letter is then sent to the participating doctor of the patient to help guide treatment.  In the letter, please note the statement, "the ultimate
criterion for dose adjustment must always be the clinical response of the patient."


Another thing to be aware of is that hypo patients often find that their body does not adequately convert the T4 med to T3, resulting in too low Free T3, and hypo symptoms.  Your doctor recognized the need to raise your Free T3.   I would like to know the ranges for both your Free T3 and free T4, as shown on the lab report.  I expect that your Free T4 is adequate,  so, instead of raising your T4 med, plus adding Armour, I think it would be better to  add some T3 med to your daily dosage.  Then the best approach is to continue to slowly increase the T3 med as required to relieve symptoms.

One thing further is that hypo patients frequently are also too low in the ranges for Vitamin D, B12 and ferritin.  If not tested for those, I really recommend doing that.  Each is very important for hypo patients.

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