In order for my free T4 to be in the higher end of the range (18+), my TSH needs to be suppressed (0.05). Interesting also to note that when my free T4 recently fell to 13.6 (very low for me, felt very unwell), my TSH climbed to a heady 0.3. I'm fairly certain that if my free T4 fellow below 10 then my TSH would probably still be under 1. Would this indicate central / secondary hypothyroidism? Is it possible to have both primary and secondary hypothyroidism together?