I'm wondering whether body size, like gender(?) might have an impact on the amount of hormones we produce?
Are there gender-based differences in thyroid hormones? If so, are these reflected in the reference ranges given by labs? I'd ask the same regarding body size?
If I were to hypothesize that there was a relationship between body size and thyroid hormone levels and that larger people generally produce higher levels of thyroid hormones than smaller people, then I'd be inclined to believe that the smaller person who's baseline TSH levels are lower than the larger person might be presumed healthy purely because their TSH falls in the 'normal range' when infact they're hypo? Likewise the larger person whose baseline levels of TSH are higher and is hypo will be diagnosed sooner as their TSH will exceed the upper limit sooner.
This is all speculation and i'm making lots of assumptions, just something that I thought about.
I hope that if there are gender/body size/ethnicity based differences in the levels of thyroid hormones, that these are accounted for when diagnosing.