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FT3 dropping when on Levothyroxine

Hi, whenever I have my thyroid function tested my FT3 always comes back low but in normal range. When I had my thyroid function tested before any medication was given it was high but in normal range. Why is this? Thank you for any help on this.

June 2014 (before medication)

TSH - 2.7 (0.2-4.2)
Free T3 - 6.7 (3.9-6.8)
Free T4 - 10 (12-22)

August 2014 (taking medication)

TSH - 0.06 (0.2-4.2)
Free T3 - 4 (3.9-6.8)
Free T4 - 15.6 (12-22)
12 Responses
798555 tn?1292791151

How much Levo per day do you take?

Were both tests taken close to the same time of the day?

At the same clinic? - If not, are you sure the ranges are really the same? Ranges vary by blood test machine used.

June to August isnt much time - maybe all this will change.
Avatar universal
There is a phenomenon associated with low FT4 levels:  the body kind of over-converts .

How do you feel with that the low FT3 level?  My FT3 tends to run very low lately, in fact below range.  This has been going on for a couple of years, and I feel well, no different whatsoever from how I felt when it was higher.  
Avatar universal
I take 100mcg of Levo a day.

No, the first TSH was taken at 11am, the second one taken at 9.20am.

Yes, same clinic.

Hope this helps.
Avatar universal
I feel more hypo with the low T3. I get cold more easily, I put on weight and I get more tired and constipated. I have no idea why.
Avatar universal
Well, T3 is the "active" form of the thyroid hormones.  It's the only form your cells can use.  So, it correlates best with symptoms.  

Your FT4 is still only at 35% of range, and the target for FT4 is about 50% of range.  This is based on where many people start to feel symptom relief.  My recommendation for anyone starting T4 only therapy is to get FT4 to a stable 50% of range, stable meaning at least two consecutive tests 4 weeks apart with FT4 levels close to each other.

While that's happening, your FT3 should be tracking it up.  The goal for FT3 is 50+% of range.  However, some of us found that FT3 lagged behind FT4 a bit and continued to rise even after FT4 had stabilized.  

After being hypo for a while, your whole body has to rebalance.  Conversion of FT4 to FT3 also has to ramp back up.  

My advice to you would be to try increasing your levo.  That might be difficult because your doctor will probably freak out over your low TSH and actually want to decrease your meds.  If you still have symptoms, you can't let him do that.  Once at about 50% of range, if your FT3 is still in the toilet, and you still have symptoms, it's time to think about adding some T3 into your meds.  That can also be a difficult proposition in the UK.  

Do you know if you have Hashi's?  
Avatar universal
I was just reading through this thread and noticed Sunny's question about the high Free T3 in her first set of labs.  It reminded me of this quote from a good thyroid doctor.  What he describes seems to answer the question.

"The free T3 is not as helpful in untreated persons as the free T4 because in the light of a rather low FT4 the body will convert more T4 to T3 to maintain thyroid effect as well as is possible. So the person with a rather low FT4 and high-in-range FT3 may still be hypothyroid. However, if the FT4 is below 1.3 and the FT3 is also rather low, say below 3.4 (range 2 to 4.4 at LabCorp) then its likely that hypothyroidism is the cause of a person's symptoms."
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649848 tn?1534637300
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1756321 tn?1547098925
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