Reference ranges

[Hollins]

A quick question while you're having your cornflakes ( or fasting for a blood test 😊) if anyone knows the answer:

Every day there are posts from people whose TFTs are within the reference range for the lab. And every day there are comments along the lines of 'your TSH / T3 / T4 should be higher within range'

How are the ranges set? Is it simple statistics? Based on this forum they don't seem to be very helpful.

Best wishes

[helvella Administrator Thyroid UK]

One of the big problems for thyroid is that the laboratory reference intervals are population statistics.

It might be true that 95% of people tested have an FT4 between (for one example) 12 and 22. But one individual might need FT4 to be between 16 and 19. And another 15 to 18.5. For them, an FT4 of 13 or 21 would be very wrong.

That is, we have set individual set points and ranges which are much narrower than the population statistics seem to show.

This is a link to a very good article in the British Medical Journal discussing what the 'normal range' really is. Very readable.

The normal range: it is not normal and it is not a range

helvella.blogspot.com/p/the...

[jimh111]

There is also a very good talk on thyroid testing by David Halsall youtu.be/Z0Z-zYF3OP4?featur...(Not working as expected?) .

[tattybogle]

healthunlocked.com/thyroidu.... difference-in-reference-ranges-reading-matter-for-a-rainy-day-.

[Hollins]

Thank you for replying. There's some weekend reading and listening for me.

Thankfully my endocrinologist is of the opinion that the individual's normal is their own correct level.

[serenfach]

Think of it like this - the normal shoe size for an adult in men's shoe size in the UK is a 9 and women's size is a 6. If you are a shoe size 7 but they gave you a shoe size 4, how would you walk around? "Normal" range for you is individual.

TSH range was first set by testing 19 men. Most of us know that we feel better when our results for T4 and T3 are towards the top of the range, and we have shared that information here for years, just to help others who may be "in range" but not well.

[Gillybean1]

Hello Hollins,

And I would agree with Serenfach and add that a few years back from my then (sadly moved on) rational GP , told me that the NHS TSH range was set using healthy young men with no thyroid disease aged 20 -22 years old . She described the range as crude and not helpful if you already have any of the thyroid diseases.

Another very elderly GP in the practice told me that she used to prescribe what we know as NDT until the symptoms improved, keeping an eye on any hyper symptoms. She said she did this until 1987, when I believe Levo came in.

Different times......., every best wish, G