TSH + Free T4
TSH makes more sense when you know what Free T4 is doing.
Pair the Signal With the Hormone
TSH reflects pituitary signaling; FT4 reflects circulating unbound thyroxine.
Together they distinguish overt, subclinical and central patterns.
Read the Combinations
High TSH + low FT4 = overt primary hypothyroid pattern. High TSH + normal FT4 = subclinical hypothyroid pattern.
Low TSH + high FT4/T3 = thyrotoxic pattern.
A 'Normal' TSH Can Still Be Wrong
Low or inappropriately normal TSH with low FT4 should raise concern for central hypothyroidism rather than reassure you.
Central hypothyroidism requires a different clinical framework than primary thyroid disease.
Check the Confounders
Acute illness, pregnancy context, biotin, medication interactions and levothyroxine timing/adherence can create discordant or misleading results.
Interpret thyroid results in clinical context, not in isolation.
Want more depth?
Read the Deep Dive