QUESTION: A question about monitoring when a patient is on T3. When a patient is on T3, I’ve been monitoring their levels 6 hours after dosing to see the highest level of T3. I want to be sure that I don’t overdose them. Is this appropriate? If you monitor them more than 24 hours after the dose, wouldn’t I expect their T3 to be low because it’s been mostly metabolized? Or would you still expect their levels to be in optimal range even 24 hours after their last dose?

ANSWER: You can test either way but if testing in the Tx window expect T3 to be high and T4 / TSH low. I wait 24 to 36 hrs later to check TSH suppression – if you are Low to -0- TSH and high T3 at 24-36 hrs then you have an overdose or nearly that. If you see a low-normal to normal TSH you are fine, and if the TSH is over 1.0-1.5 you are probably underdosing. Trying to bracked T3 dose and hit the sweet spot of plasma level is tricky, and in my experience almost always leads to under-dosing.

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