TSH - T4L - T3L salad - USMLE Forums
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Old 04-29-2011
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Thyroid TSH - T4L - T3L salad

Hello again
I have a salad in my head and I hope someone can help me solve my problem.
I learnt that in hypothyroidism, TSH goes up first then FT4 starts going down and in the very severe cases, FT3 follows too.
Hence, the classical algorithm opting for TSH-FT4 dosage looks very logical with a very null role of FT3 dosage.

My problem lies in the hyperthyroidism case, in which TSH seems to go down first then FT3 (!) up before FT4 this time!
My question is: why do classic algorithms still prefer TSH-FT4 dosing in this case? especially in suspected sub-clinical hyperthyroidism?

I read somewhere that FT3 is a reliable indicator of all sorts of hyperthyroidism (not only T3 hyperthyroidism), and therefore can be dosed unorthodoxly after TSH to confirm the diagnosis.

Please correct me if I'm wrong and explain to me why is the TSH-FT4 combination always chosen first no matter what the thyroid problem is.
Thank you
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Endocrine-, Pathology-, Physiology-

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