Does serum free T3 fall before free T4?

Long story short: I usually feel best with TSH well below the bottom of the reference range and free T4 at about 18-20. Bloods done last week confirm that these values are holding, but that free T3 was well down at 3.8 (3.5-5.5), which may account for why I feel quite so crappy.

The question is this: if I were to retest in a week or two, would you expect the free T4 to have fallen too? In other words, does the serum free T3 value usually (but not always) fall before the free T4 does?

8 Replies

  • Hose, yes when T3 falls the pituitary pumps out TSH to stimulate the thyroid gland to produce more T4 for conversion to T3.

  • Cheers, Clutter. Blimey, do you ever sleep?

  • Not last night, hose, despite a sleeper :( I'm yawning now so will probably fall asleep when something interesting is on the radio.

  • My sympathies. The rare nights when my amitriptyline fails are just awful.

  • Hose, if I don't nap too long I'll sleep long and deep tonight.

  • If you are on levothyroxine, what you are describing is common. Both TSH and T3 should drop when T4 levels out, as shown in this graphic:

  • Thanks, HIFL. I'll have a read.

  • Hi Hose, What I get is as I raise the thyroxine dose,am on 75 now,I am seeing that my FT3 falls also,as does my FT4 slightly.they are all still in 'range' and I feel ok but I have often wondered why that happens cos all advise seems to be that FT3 should rise with more levo and lower TSH. I dont get it half the time!

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