For people not on any thyroid med:
Its a combination of looking tsh t3 t4 together. If TSH is off, its because t3, t4 or both are off, which is why you need to test all. If just one is off....it depends how far off, it opinion then.
With most people low t3 or t4 will raise tsh (hypo), the degree of which this happens can vary a little between people, which is why its best to look at all three.
Some people dont convert from t4 to the active t3, which is not uncommon. Supping with t4 med wont help these people. Tell that to a Dr who only saw a slightly low TSH, but didn't bother to find out why, or just supped with synthetic t4 med.
Remember, t4 and t3 are cell fuel/food, not tsh.
Thyroid is most closely related to adrenals. And adrenals can effect free blood glucose levels- "glucose dumping" from liver by the adrenal signal for more energy- even if your resting BUT under stress. Yes..stress kills.
Post Edited (astroman) : 9/15/2018 4:15:57 PM (GMT-6)