Hi,
decreasing FT4 or Total T4 in normal limits or below normal limits ??
what about
TSH..??
See If low FT4 and Total T4and TSH high you need to start on thyroxine replacement ( Hypothyroid treatment)
if Low FT4 , low total T4 and low TSH ----> then you need to work up your pituitary gland status in brain
and also need thyroxine replacement
need detailed history and examintation
Next Steps
Consult endocrinologist