New Reference Ranges

[Ktlc]

hi - In preparation for my endo meeting tomorrow I was digging around and found this:

nbt.nhs.uk/severn-pathology....

Note new reference range for FT4 from 10/05/24: TSH: 0.38 -5.33 mU/L, Free T4 8.0 – 18.0 pmol/L, Free T3: 3.8 – 6.0 pmol/L. See document below for Reference Ranges in Children (ages 0-18 years). If replaced with T4 ideally TSH should be in the reference range unless suppression is required e.g. Thyroid cancer. In pregnancy the following ranges apply: 1st trimester TSH 0.05 – 3.70 mU/L, FT4 6.7 – 13.9 pmol/L; 2nd trimester TSH 0.31 – 4.35 mU/L, FT4 5.8 – 12.7 pmol/L, 3rd trimester TSH 0.41 – 5.18 mU/L FT4 6.2 – 12.2 pmol/L.

[SmallBlueThing]

In the first quarter of this year, the range for TSH in my area changed from [0.3 - 5.0] to [0.55 - 4.78] mIU/L. My TSH has been higher than previously, so I've not seen if there's a change to the range for fT4, which gets tested when TSH < 1.0 or above range.

The lower end of the range for serum calcium was raised a few years ago, meaning even more people with "mild" yet symptomatic hypocalcaemia will be left without answers.

[BenLabrador]

Thanks for this.

[helvella Administrator]

While reference intervals (ranges) often appear set in stone, the reality is that changes are actually quite common.

When I first started to see TSH tests from those in the UK, they often went up to 6 and more.

One of the reasons was the failure of those setting the RI to ensure that all samples used in the process were from people without any known thyroid issues. A second factor was that they were more prone to interference from certain antibodies. Together, these factors made it look as if higher results were still acceptable.

Since then, I think all UK labs will have re-set their RI for TSH - at least.

Changes can result from several things including change of technology used, e.g. a new analyser, re-assessment and review.

[DippyDame]

The ref ranges may change, but, calculate the %age of result (TSH, FT4, FT3) through the ref range and that should be fairly constant

Quick calculator

thyroid.dopiaza.org/?utm_so...

[Ktlc in reply to DippyDame]

thanks. I do use the calculator but I can’t find the post that said what the % should ideally be. I thought I’d saved the post but can’t find it. Thx

[helvella Administrator in reply to Ktlc]

There really is no % your result should be.

This is a means of comparing your results when they were reported with different reference intervals - whether from different labs or when a lab's reference intervals change.

That is, if your FT4 was at 70% when you were OK then another test could be expected to be near 70% even if the reference interval is different.

You might be good at 70%, someone else might be good at 60%, 75%, 83% or whatever. But it really isn't a matter of comparing yourself with others.

Any "should be over 50%" is very, very approximate.

And this sort of approximation is still only that - an approximation.

[Ktlc in reply to helvella]

That’s great. I’m feeling very good at the moment and my exercise intolerance has passed. Occasional flare ups and my % are

TSH -7.3% (<0.01)

FT4 76%

FT3 86%

Fortunately for me I deal with the endo not the GP so he isn’t planning on reducing my Levo based on TSH

[helvella Administrator in reply to Ktlc]

If those percentages work for you, then you have a yardstick for the future. Just don't expect it always to be absolutely spot on - a few percent either way is well within the variability to be expected.

[DippyDame in reply to helvella]

...thanks helvella