Reference interval of thyroid stimulating hormone and free thyroxine in a reference population over 60 years old and over 80 years:

[Clutter]

...comparison to young subjects

Results

TSH increased with age in the whole group. There was no statistical difference in the analysis of these independent subgroups: 20–49 versus 50–59 years old (p > 0.05), and 60–69 versus 70–79 years old (p > 0.05). Consequently, we achieved different TSH RI for the three major age groups, 20 to 59 years old: 0.4 - 4.3 mU/L, 60 to 79 years old: 0.4 - 5.8 mU/L and 80 years or more: 0.4 - 6.7 mU/L. Conversely, FT4 progressively decreases = significantly with age, but the independent comparison test between the sub-groups showed that after age 60 the same RI was obtained (0.7 - 1.7 ng/dL) although the minimum value was smaller than that defined by manufacturer. In the comparison between TSH data obtained by this study and those defined by the manufacturer (without segmentation by age) 6.5% of subjects between 60 and 79 years and 12.5% with 80 years or more would have a misdiagnosis of elevated TSH.

Conclusions

TSH normal reference range increases with age, justifying the use of different RI in subjects 60 years old and over, while FT4 decreases with age. Using specific-age RI, a significant percentage of elderly will not be misdiagnosed as having subclinical hipothyroidism.

thyroidresearchjournal.com/...

[chihiro]

That's really interesting. Thanks for posting Clutter. Do you think it is just down to the simple thing that as you get older your body works less efficiently so that obviously includes the thyroid?

[helvella in reply to chihiro]

What is NOT obvious is how come, in this less efficient body, the pituitary goes in the opposite direction and manages to pump out more TSH.

The article suggests that lower FT4 (and, probably, lower FT3) may confer advantages in the elderly. Why, then, does the pituitary increase its output in an apparent attempt to restore the FT4/FT3 levels?

The elderly are very well known to have poorer digestion - which makes absorption of iron, B12 and numerous other substances less efficient. Could these things, which are so widely seen to be low in hypothyroid people, actually be affecting the elderly under investigation?

Please, researchers, make a better attempt to cover the ground before seeming to jump to conclusions. They might be absolutely right - but I am not yet convinced.

Rod

[Clutter in reply to helvella]

Good point. Back to the gut, then?

[Clutter in reply to chihiro]

I would have thought so, but as Rod says, why does TSH become more efficient?

[chihiro in reply to Clutter]

Oh yeah that's a point. Hmmm man this stuff is complicated,that is why it always stuns me when doctors try to convince you that thyroid is simple and straightforward!

[Clutter in reply to chihiro]

Their simplistic view is indicative of their sheer ignorance!