same labs but different ranges? Same tests

[Twixandolive]

same labs did both my thyroid test but the ranges have changed in one month is this normal?

[GlowCoach Administrator]

If thats One Day Tests they did change their range a while back to be more in line with other UK labs. You could always email them to ask about it.

[Twixandolive in reply to GlowCoach]

This was done Feb 2025 and March 2025 so only a month 🫣

[GlowCoach Administrator in reply to Twixandolive]

Thats frustrating but if you use the calculator you can work out the % thrugh range for both and compare.

thyroid.chingkerrs.online/

[Twixandolive in reply to GlowCoach]

Feb ratio 0.657

March ratio 2.326

[helvella]

It happens all the time.

Potentially, each analyser machine in each lab could have its own reference intervals (ranges).

And these reference intervals could change due to re-establishing them. Which might be done because of changes to machines (e.g. a new analyser), changes to the materials used (e.g. reagents), advice from the manufacturer, or simply because the lab has a schedule of checking every so often.

Typically reference intervals do not change often. Like every few years rather than months. But from what you have said, they could have been using the old ones for ten years or longer! And they might use the new ones for as long again.

From what you have posted, I cannot see what the reference intervals were before they changed.

Regardless where they are numerically, if we are attempting to compare, we can only look at how far through the reference interval our result lies. Which you can do using one of our calculators.

Thyroid Test Results Calculators

healthunlocked.com/thyroidu...

Free T4 (fT4) 13 pmol/L (12 - 22) 10.0%

This is very much a case of using what we have. None of this is perfect. But nor are any blood tests.

10.0% through FT4 reference interval is pretty low.

[Twixandolive in reply to helvella]

I have added the ratios

Between the two

I am so confused

I have lost faith in my blood results

Going to do again with a private test mentioned on here by slow dragon

I should not get the huge changes in the T3 it’s quiet a change wondering if labs have been rushed

You get results next day?

[helvella in reply to Twixandolive]

Can you post the TSH, FT4 and FT3 results from February? Including the reference intervals at the time.

Lab results like these can be achieved within a few hours. Whether your sample gets to the lab quickly enough, and whether the results get back to you in time, is another matter. But I have seen results from a lab on the same day as the blood was drawn.

[Twixandolive in reply to helvella]

Feb bloods

8:15 fasted day 14 cycle

TSH 2.73 range 0.27-4.2

FT3 1.38 range 2.02-4.43

FT4 0.907 range 0.93-1.71

March blood

8:15 fasted day 15 cycle

TSH 1.649 range 0.55-4.78

FT3 5.59 range 3.1-6.8

FT4 13.0 range 12-22

[helvella in reply to Twixandolive]

Ah!

They were using ng/dl. Your new results are in SI units.

You cannot jump between the two, especially when looking at ratios.

The lab appears to have pretty much changed from units of mass per volume to SI units which a re moles per volume.

I have converted the reference intervals and your results for February.

For FT4:

0.93 ng/dl = 11.91 pmol/L

1.71 ng/dl = 22.0111 pmol/dl

Your result, 0.907 ng/dl = 11.6749 pmol/dl.

For FT3:

2.02 pg/ml = 3.1029 pmol/l

4.43 pg/ml = 6.8049 pmol/l

Your result, 1.38 pg/ml = 2.1198 pmol/dl

February:

Free T4 (fT4) 11.67 pmol/L (11.91 - 20.0111) -3.0%

Free T3 (fT3) 2.1198 pmol/L (3.1029 - 6.8049) -26.6%

T4:T3 Ratio 5.505 

March:

Free T4 (fT4) 13.0  pmol/L (12 - 22) 10.0%

Free T3 (fT3) 5.59 pmol/L (3.1 - 6.8) 67.3%

T4:T3 Ratio 2.326 

If I have done that correctly, your FT3 has gone up significantly, which reduces the FT4:FT3 ratio.

But your FT4 is right at the bottom of the reference interval.

I have not looked at your history or what you are taking.

[SlowDragon Administrator]

work out results as percentage here

thyroid.chingkerrs.online

[Twixandolive in reply to SlowDragon]

So both sets of tests are in different ranges

I am so confused now

So will be my gp 🫣

So I put both sets in this result percentage thing and then what should I do with this

Should I test again at same place or try a new lab?

[Twixandolive in reply to SlowDragon]

Feb 2025

Results in the chingkerrs

T4:T3 ratio 0.657

March 2025

T4:T3 ratio 2.326

[GlowCoach Administrator in reply to Twixandolive]

What were the free hormone results?

What were you taking for each test - levo/ T3? How much.

How did you take the test - time of day, last dose of Levo/T3?

[Twixandolive in reply to GlowCoach]

No Levo taken

Both tests 8:15 morning both fasted both day 14 cycle

I don’t take anything at all nothing currently

[GlowCoach Administrator in reply to Twixandolive]

If you dont take any Levo then the conversion rate isn't relevant.

Thyroid numbers will naturally fluctuate firstly throughout the day but also from day to day if you are not on replacement therapy.

Its more important to look at FT4 and FT3 at this point plus TSH.

[SlowDragon Administrator in reply to Twixandolive]

let’s Get checked home test in Jan 2020

TSH 2.57 range 0.27 - 4.2

Free T4 (fT4) 13.2 pmol/L (12 - 22) 

Ft4 12.0% through range

Free T3 (fT3) 4.6 pmol/L (3.1 - 6.8) 

Ft3 40.5% through range

[Twixandolive in reply to SlowDragon]

What does the percentage through range mean?

I don’t really understand and I don’t think my gp will

The pattern I see is that FT4 is low end and the TSH isn’t rising inline with this

My TSH should be more closer to 4? With the low T4 my FT4 has been 12-13 for past 4 years

But my TSH has always been low to normal never got up near top

Dec 2020 I had nhs TSH and it was 3.36

NHS range

Had all the symptom

I then tested twice in 2021

And now back to testing again as symptoms becoming more troublesome

[SlowDragon Administrator in reply to Twixandolive]

Results suggest TSH is sluggish and not responding adequately to low Ft4

Hence the suggestion of central hypothyroidism

[Twixandolive in reply to SlowDragon]

This has been like this a few years now

I am doing a full bloods again also full female hormones

Requested my maternity notes to see if I lost a lot of blood I was very anaemic after had a very traumatic first birth I have low blood pressure so if my blood pressure was very low in birth maybe some links to Sheenans syndrome

As I didn’t produce milk with either pregnancy

My testerone has been constantly low past 4 years

Symptoms are now quiet difficult to ignore

And my last two thyroid test as at bit all over the place

Central hypo looking very likely

Going to hold off Levo for another month wait for next bloods

Then I need to see a central hypo specialist

Xx

[humanbean]

What does the percentage through range mean?

Suppose you test something called X.

Your result is 15, and the reference range is 10 - 20.

15 is half way through the reference range so your result is 50% through the range.

If reference ranges are different from one machine to another, then the percentage through the range should make it possible to compare. If your result is 50% through the range on one machine then it should never be 85% through the range on another machine. It should be roughly 50% on another machine too, even if the reference ranges are different.

Using percentage through the range allows for comparisons between two different results. So even if two tests have different reference ranges you can say, "My result from two months ago was 50% through the range, and my most recent result was 72% through the range so it is rising. If your most recent result was 42% through the range then your result is dropping.