Interesting.... Uk test results may depend on which lab they are sent to

[AKatieD]

Just got an email from Medscape with the letter below. Nice short read.

academia.edu/96303687/Diffe...

Researchers in Wolverhampton found that TSH and T4 results varied massively depending on the assay system used by the labs concerned. 2 systems being used by 75% of uk labs. The differences were not fixed by the use of different reference ranges.

Another reason to only use lab results as a guide.

Maybe worth finding out which system the labs of the blood test providers use, or even if they always use the same lab with a particular system.

[tattybogle]

yes, if the level is close to the top / bottom of range , then the differences between various assays used can be large enough to make the difference between being within range /or not . hence which assay is used will affect whether someone with borderline results is diagnosed as 'subclinical' . or told 'normal' . And also whether someone taking thyroid hormone replacement with top end fT4 level is told 'ok carry on' , or 'reduce dose'..... just because the lab is using an assay manufactured by 'x' or 'y'

the article you posted looks at assays made by Roche ,and Abbott ....there is another one that 2 or 3 NHS labs currently use , made by Beckmann- Coulter , which has an unusually low /and narrow fT4 range of about [7.9 -14].... actual range varies slightly as it is adjusted locally , so you may see [7.9 -14.4] etc .

my lab uses this now ( previously used 8-18), and i took an interest as i was getting higher/ over range fT4 levels. so i collected some stuff of interest here: healthunlocked.com/thyroidu.... difference-in-reference-ranges-reading-matter-for-a-rainy-day-.

Since looking into the issue i have come to the conclusion that all thyroid blood results ( especially fT4 ) need to be viewed as " in the ball park of" rather than an absolute truth.

[AKatieD in reply to tattybogle]

Definitely. Reference range less definitive than I realised.Would be interesting to know what Medichecks, Blue Horizon etc use and if it is always the same system too ( never get NHS tests)

[helvella in reply to AKatieD]

I suggest you email and ask!

They might find it a little difficult to be definitive as they could well use more than one lab.

(Technically, one lab could have two analysers from the same company but actually use slightly different reference intervals for each machine.)

[AKatieD in reply to helvella]

Hi again.It seems that the main private testers all use Roche. That is MMH, Medichecks, Randox, Thriva, Blue Horizon.

Although Randox customer service was slow and annoying, saying they also use another system sometimes but it would not say when or how you could tell which one had been used.

So it seems that the Roche range of 12 - 22 (25% higher than Abbots 9-19) for T4 is going to be the one most of us see, since some of the NHS use Roche too.

Also the Roche results are 16% higher than Abbott ( hence the higher range) so you need to be careful comparing when your results have different systems or if they fall at either end of the range.

[helvella in reply to AKatieD]

diogenes wrote a relevant post about three years ago:

Can't trust thyroid assays in SCH

healthunlocked.com/thyroidu...

[AKatieD in reply to helvella]

Indeed, the best we seem to be able to say is that most providers are going to be consistently inaccurate.

No idea why they can't work out what the correct figure should be and fix their assays accordingly.

Does not inspire confidence!

[AKatieD]

I will return with some info if I can obtain it!

[Eos333]

Hi all, just wanted to ask as I am having the same issue. I am on Levo for 2 yrs and cant get it right. NHS GP's shows within range FT4 of 16 ( 9-23) but then on 2 private labs is 22.9 and their range is 12-22 and dont know who to trust. My private Endo wants to give me T3 instead but NHS wants to increase the dosage as I am well within the range for FT4 but still TSH IS 6.80 and on private is 8.90. I am still waiting for NHS Endo to have second opinion as NHS don't like to give T3 . Anyone expereinced the same or maybe can give me different option I can check as NHS and Private labs have massive difference on FT4 which makes it difficult for medication as one says undermedicated the other overmedicated. Thank you

[tattybogle in reply to Eos333]

unless the samples were all from the same blood draw , the differences could be (more or less) correct.

2 samples from same blood draw sent to 2 different labs is the only way to prove there really is a significant difference.

[Eos333 in reply to tattybogle]

Hmmm that might be tricky to do. But as per the post below I did mentioned it was about 50mins difference anyways which should be that drastic difference in the results I should think. 🤔

[AKatieD in reply to Eos333]

Just a suggestion if it arises in future...If you go to NHS test appt, just ask phlebotomist to fill the private tube at the same time. They have been happy to do that in past and saves you the private blood draw fee.

[Eos333 in reply to AKatieD]

Thats a good idea too - thank you. Yeah I should ask. Btw when my blood was drawn at NHS GP they've told me actually the most acurate results are at NHS ones and even private hospitals they are using it apparently. Not sure how true is that as my private Endo doesn't trust it but just wanted to mention.

[AKatieD in reply to Eos333]

Sounds like PR guff to me, but happy for anyone with experience to the contrary to correct me.

The paper in the link at the top was written by NHS staff and suggests most of them use the same systems as the private companies (the firms I have contacted all say they use the Roche system as in the report so far, just waiting for Randox to reply before confirming to the group).

[tattybogle in reply to Eos333]

oh i see , yes.

i have similar instance of ft4 results differing more than would reasonably be expected.

45 mins apart (gp test > cycled gently home > did fingerprick)

both done using NHS hospital labs , so ' private labs not as reliable' simply doesn't cut it as reason here :

GP (phlebotomist blood draw. sent by van to Lancaster hospital lab)

11am fT4 15.7 [7.9-14] significantly over range (Beckmann-Coulter assay is used here)

TSH 2.65 [0.57 - 3.6]

Monitor My Health (nhs run fingerprick /postal service, sample posted to Exeter NHS hospital lab ).

11.45am fT4 22.1 [12-22] a 'gnats' over range ( don't know what assay used here )

TSH 2.9 [0.27-4,2]

not really enough difference to kick up a stink about , and technically it's different methods fingerprick / veinous ,plus 45 mins apart , so complaining wouldn't go anywhere ,, but i'm keeping this example up my sleeve for next time i need to argue about fT4 levels with GP.

next time i get GP blood draw i'll be asking phlebotomist nicely if she can fill up the MMH tube at same time to eliminate the 45minute difference .... if i still get such a big difference then i might contact the labs directly.

post with some info about testing : healthunlocked.com/thyroidu.... healthunlocked.com/thyroidu....

[AKatieD]

Same private tester for the two or different?

[Eos333 in reply to AKatieD]

Two different private testers ( HCA Hospital and Thriva )

[AKatieD]

Well at least those 2 private tests are consistent, which is what you would hope for. Thriva have told me they use the Roche system but I was not aware of HCA so had not asked them.

We also don't know what system your NHS lab used. But that difference between NHS and private is ridiculous.

I assume they were all done first thing in morning, fasting, and after similar amount of time/ dose of your last thyroid meds?

[Eos333 in reply to AKatieD]

Yeah dont know. The blood draw were in similar times at around 13:00/14:00 o'clock and not fasting and Levo taken around 8:30am in the morning. Yeah dosage the same on Levo. It could be maybe because of the ranges as NHS has wider range ( 9-23 ) and private has shorter range ( 12-22 ) unless is that. So on Private (HCA) the result were 22.8 and on NHS 16 of FT4 and that is only like an hour difference as I wanted to make sure I do the blood draw at as closer time as possible for both in the same day. That was 13:10 at NHS and 14:00 o'clock at HCA same day.

[AKatieD]

Even accounting for the difference in range, they still look very different- private top of range, NHS mid range. NHS being first would suggest that your hormone levels climbed substantially over the 50 mins.

Probably a reason to stick with the fasting, 8-9am, before meds, idea as then you remove a bit of potential for variation over the day.

[Eos333 in reply to AKatieD]

Yeah thanks. I'll book another test for Thriva for example as there don't need referral ( done through Superdrug) and do test early morning with fasting before the meds. If test shows consistently same as before then I would think is not the fasting that causes it etc. Or maybe I shoukd go for NHS and ask them again but because I have done recent blood test with them they might say I have to wait 6 weeks again.🙄

[AKatieD]

Yes, NHS will probs say wait and maybe hard to get early appointment

[sparkly]

You don't even need to send to different labs to get different results Some years ago I had blood taken for my endo appointment, but gp also requested them. Nurse took 2 lots and sent to hospital lab.

They both came back differen. One test had my ft3 at 5, the other had it at 4.6, the ft4 was different too

Tests were done a couple of hours apart but must have been performed on different machines that obviously wasn't calibrated the same.