Shocking blood test result variation: NHS Vs Private UKAS laboratory 😳

[Agitator23]

One day apart:

NHS fasting 10.30am. 2/09/24

TSH 0.06 0.35 - 4.94 minus 6.3%

Free T4 16.4 9-19.1 73.3%

Free T3 5.2 2.4-6 77.8%

PRIVATE fasting 12pm. 3/09/24

TSH 0.046 0.4 - 4.05 minus 9.7%

Free T4 16 10-28 33.3%

Free T3 5.4 3.5-9.46 31.9%

So, long story short(ish). (More in my bio). Diagnosed as hypothyroid after many years battling with a 'mystery illness'. Primary hypothyroidism diagnosed via ultrasound and secondary hypothyroidism diagnosed by multiple NHS and private blood tests over a period of a year.

Trial on levothyroxine 50 mcg by GP in June 2024. (NHS endocrinologist still adamant not thyroid problem). Private endocrinologist (specialist thyroid) believes central / secondary hypothyroidism. Told me to immediately double dose to 100 mcg.

Been on 100 mcg levothyroxine for five weeks. Feeling great improvements - energy, skin, eyesight, digestion - the lot. Best I've felt in a decade. Feel this vindicates the diagnosis of hypothyroidism. Definitely not hyperthyroid on this dose and no side effects.

Having my follow-up appointment with private endocrinologist next week so had blood tests at the GP surgery but also decided to have private blood tests at a clinic near me.

I've been using this same private clinic and having occasional NHS tests over the last year. There is a pattern of the NHS tests being different to the private clinic test results. The private clinic uses a lab that is also used by the NHS.

The NHS blood test results have consistently shown higher thyroid hormones than the private clinic blood test the differences were not huge but significant enough for me to finally get diagnosis. (I have tabulated all these results and will attach in my bio).

BUT ... Now this! I'm completely shocked by these results. Which is right?! These tests are only one day apart. How do you dose adjust based on these?

NHS fasting 10.30am. 2/09/24

TSH 0.06 0.35 - 4.94 minus 6.3%

Free T4 16.4 9-19.1 73.3%

Free T3 5.2 2.4-6 77.8%

PRIVATE fasting 12pm. 3/09/24

TSH 0.046 0.4 - 4.05 minus 9.7%

Free T4 16 10-28 33.3%

Free T3 5.4 3.5-9.46 31.9%

Absolutely unbelievable! One indicates not to increase dose and the other indicates an increase of levothyroxine is necessary. My GP called me and was about to reduce my dose to 75 mcg. Luckily my private endocrinologist had said in a letter to the surgery that the aim was to get my FT4 to 19 or 20. Obviously, 20 will be outside the range that the NHS blood test specifies above 🙄 The endocrinologist did not mention the range or percentage when saying our aim was 19 or 20.

My GP didn't ask how I was feeling or about my symptoms but I reminded him of the endocrinologist letter. He is leaving me on 100mcg.

I'm seeing the private endocrinologist next week. What do I do about the huge difference in blood test results? I feel like the private tests are more reliable based on my severity of symptoms over the last year and the private blood test results.

How terribly unscientific and what a complete mess the diagnosis and treatment of thyroid dysfunction is! On the face of it both tests show FT4 as 16 and 16.4 - but how different percentage through range and how different the treatment would be! These laboratory ranges are incredibly different. Why?

Which do I show to the private endocrinologist? I feel I need to follow this up but not sure how. I think I should go with how I feel symptom-wise but GPs seem to act on the blood test results alone...

Very annoyed and very confused 😕 This TF blood test madness needs to end. There needs to be standardisation of reference ranges across all labs. *Deep sigh*.

[SlowDragon Administrator]

Been on 100 mcg levothyroxine for five weeks.

Increasing by 50mcg per day is a large increase

Generally will increase by 25mcg daily at any one time

Testing should be minimum 6-8 weeks after increasing dose

After increasing from 50mcg to 100mcg better to wait 10-12 weeks

Essential to test vitamin D, folate, ferritin and B12

When were these last tested

What vitamin supplements are you taking

ALWAYS test early morning, ideally before 9am and last dose Levo 24 hours before test

Many people find different brands of levothyroxine not interchangeable

Which brand is 100mcg

Which brand was 50mcg

[Agitator23 in reply to SlowDragon]

Hi SlowDragon

Yes. I was a bit concerned about doubling the dose due to what I'd read on here but the endocrinologist was insistent.

It's been a brilliant experience so far. I can't believe the difference. The brands are the same - Teva just a different dose.

The problem is the vast difference between the FT4 reference range used by the GP surgery - 9 to 19.1 - and the private UKAS laboratory, 10 to 28! The pmol/l analysis is almost identical, FT4 16 and 16.4, but the choice of range makes decisions on dosing impossible. How can I be 33% and 77% for FT4 at the same time?

[SlowDragon Administrator in reply to Agitator23]

How long before test was last dose levothyroxine

My GP is going on the NHS lab saying I'm too high

As your Ft4 is well within range on NHS test and about perfect at around 70% ignore GP

[Agitator23 in reply to SlowDragon]

Both tests were just over 24 hours after last dose.

My GP writes "central hypothyroidism" with that punctuation in my medical notes. Not sure why. Still not in my medical record that I'm hypothyroid.

He is listening and he is trying to do the best he can. I can feel his unease at stepping outside his comfort zone. He's also feeling that he's missed this diagnosis for the past decade... He did in that time, however, send me to every consultant under the sun - except an endocrinologist!

[SlowDragon Administrator in reply to Agitator23]

When TSH doesn’t increase as Ft4 and Ft3, this is central hypothyroidism

Medics think it’s very rare ……it’s not

It’s just rarely diagnosed

Central hypothyroidism

bestpractice.bmj.com/topics...

ncbi.nlm.nih.gov/pmc/articl...

endocrinologyadvisor.com/ho...

academic.oup.com/jcem/artic...

ec.bioscientifica.com/view/...

academic.oup.com/jcem/artic...

Low vitamin levels tend to drop as Ft4 and Ft3 fall, because low stomach acid as result of being hypothyroid results in poor nutrient absorption

Low vitamin levels tend to result in poor conversion of Ft4 to Ft3 …..this results in higher Ft4 and lower TSH

[Wua13262348 in reply to Agitator23]

Unlikely it would have helped if he had referred you. My FT4 has been MINUS 65%, and my health board has told me I definately don't have Central Hypothyroidism, as they would like an FT4 of 1 or 2 for that!!!!! My FT4 was 5.5. In a letter to my G.P. I would never have had access to had I not been given a copy of it as a Private Endo appointment required a G.P. referral, they have written "possible Central Hyperthyroidism." Yes, HYPER!!!!!!!!

I definately do have Central Hypothyroidism per The Persani guidelines you previously posted about, complete with genetic cause cited in Persani. The 20% drop or more in FT4 cited by Persani , for me , was an almost 50% drop. Two years after this it dropped another 50% further than the original 50% drop.

My health board has Guidelines for Central Hypothyroid for Primary Care G.P.s so it is not as if they don't know about it. You can find them on the internet.

You couldn't make this up!!!!

[HealthStarDust in reply to Agitator23]

One of my FT4 was tested twice by the same lab from the same sample and both had different results (it was via my GP too). It’s not unusual. Hormones and their blood tests are very fickle.

[Agitator23 in reply to HealthStarDust]

I agree. I'm rather shocked by the choice of reference ranges, though! The actual measurements in pmol/l seem accurate but the choice of range is all over the place 🙄

[jimh111]

The results are virtually the same, they simply have different reference intervals. The private lab has very wide intervals which suggests they don't screen their reference population very well. The percent figures shouldn't be used to give a false indication of precision, they tell you more about the reference group than the individual patient.

[Agitator23 in reply to jimh111]

My GP is going on the NHS lab saying I'm too high and my endocrinologist wants me at 19 or 20 for my central hypothyroidism... I foresee an ongoing conflict!

[jimh111 in reply to Agitator23]

Your GP is going by TSH because that's what endocrinologists have told them over the years. If your endocrinologist says you have central hypothyroidism then get them to write to the GP saying this and telling them they should disregard TSH.

[Agitator23 in reply to jimh111]

I'm adding that to my list of asks when I see the endocrinologist next week. Many thanks.

[helvella]

The tops of the reference intervals for the free hormones at the private lab look to be VERY high.

I'm not convinced that percentages make any sense for TSH below bottom of TSH reference intervals. And my view is that the difference between 0.06 and 0.046 isn't that great.

Rather than appearing as reflecting the known and expected variations between labs, that private lab appears to have extended the top ends of the reference intervals for FT4 and FT3 by a considerable margin compared to other labs.

They might think they have a justification for this, but I am sceptical that their results can be compared on a percentage through range basis. Given that your actual numeric results are fairly similar, that reinforces the appearance of their tops of ranges being high. Possibly unwarrantedly so.

And you are quite right, doctors across the universe tend to talk of targetting numbers without any apparent appreciation of different labs, ranges, etc. I suspect they simply bring to mind whatever they most often see.

If I were you, I'd avoid basing anything on those high top of range numbers. But I would contact the lab and ask them:

What analyser they are using;

What their historical reference intervals have been;

How they justify their ranges being so different to other labs and their advice on how to compare results. (They might duck this with respect to other current results. But if their ranges have changed, it is entirely reasonable to expect an answer with respect to their OWN historical ranges.)

[Agitator23]

Great idea to contact the lab. I also think 28 as top of the range is too high. I think I'm going to go for the NHS reference range from just a few years back, 9 to 24. They used this in a 2014 blood test I had. However, this situation with ranges now means my private endocrinologist, who wants me to get to 19 or 20, is going to be at odds with my GP who is using the 9 to 19.1 range. (Apparently, for Central Hypothyroidism they try for a higher FT4 than usual).

[Wua13262348 in reply to Agitator23]

My private Endo told me to drop from 72mcg T4 to 50 mcg and add in 15 mcg T3. That doesn't seem to be targeting FT4 of 19 or 20, in my particular case. To be fair though, I have serious doubts that this will work for me!

[Wua13262348 in reply to Agitator23]

I don't think anyone will bother looking at, or noticing, the different ranges of the 2 tests. FT4 and FT3 in both tests are practically the same. The private Endo I consulted , I found , treats percentage through the range results, like a red rag to a bull!!! He did however want both the reading and the range. It looks as if you should just consider both tests to have had the same result and ignore the range. I would base it on the NHS range and consider yourself to be the 70 odd% through the range, if it were me, if that is any help.

[Sleepman]

Nice that ratio of T3 to T4 is similar, looks like you are an OK converter on this one set of tests. Fingers crossed for you.

I went from 50 to 100 mg nearly 2 years ago and was ok.

I tracked my pulse and blood pressure.

[Agitator23 in reply to Sleepman]

Thanks. My next question was going to be about the T3:T4 ratio... Pulse and blood pressure good.

[pennyannie in reply to Agitator23]

We generally feel best when on T4 monotherapy when the T4 is up in the top quadrant of its range at around 80% with the T3 tracking just behind at around 70% :

On the NHS test your T3 is higher than your T4 -

do you feel as though your metabolism is running a little fast ?

The Private blood test has your T3 and T4 the right way round but much lower in the ranges.

Maybe start monitoring your blood pressure, pulse and body temperature AM and PM just to try and understand what your body is doing ?

Once the T4 is up / towards, the top quadrant of its range, the accepted conversion ratio is said to be 1 / 3.50 - 4.50 - with most people feeling at their best when they come in this ratio at 4 or under.

So on the NHS test we are looking at a conversion ratio of 16.40 divided by 5.20 = 3.15 :

With the Private test with a T4 at 16.10 divided by a T3 of 5.40 this makes a slightly faster metabolism at 2.98 - say - 3.00 :

So not much of a difference - but maybe you are running a little faster ?

[Agitator23 in reply to pennyannie]

Thank you for the advice. I'm a bit hazy on the ratio side of things. Don't feel I'm running fast. I think I'm naturally nearer the top of the range (whatever that is!) I'll keep a check on pulse and blood pressure.

[waveylines in reply to Agitator23]

Tbh the optimum level is where you feel at your best either no symptoms or very low. Everyone is a bit different. Percentages are to be used as a rough guide. It is not an exact science. Most important to ensure the co factors are optimal for best results.

I always do temp and pulse rate first thing as another way to cross check, another guide used years ago before blood tests.

[Agitator23 in reply to waveylines]

I agree. The problem is convincing my GP that I feel fine when the lab uses a reference range (and therefore percentage) to say reduce dose... I'd like to just choose which reference range to use but my GP is stuck with 9 - 19.1!

[waveylines in reply to Agitator23]

Do GPs use percentages then? That's news to me.. Mine just went on TSH (theyre not allowed to test ft4 or ft3 anymore lol) and as my TSHs been suppressed for years thats rather pointless!! Lol

[Agitator23 in reply to waveylines]

Hi. No, that's just me trying to make sense of things. It's been really helpful in seeing the central hypothyroidism pothyroidism. It showed my GP that over the past year how my TSH hardly moved as my fT4 fluctuated and fell significantly... The private endocrinologist agreed central hypothyroidism.

My TSH reading is now pointless and will always be flagged by the lab and the low top end of fT4 range means the lab will always say I'm overtreated - when I'm not.

[Bluesadawg in reply to pennyannie]

sorry if this sounds dull, but what does blood pressure, pulse & body temp tell us? Is this to do with hyperthyroid/ too high doses of levo?

[waveylines in reply to Bluesadawg]

Blood pressure often increases wurh hypothyroidism and reduces as treated. Temperature drops with untreated hypothyroidism but increases back into your normal range once we'll treated. Pulse first thing before riding will often be low when untreated, once treated optimally will normalise.

[pennyannie in reply to waveylines]

Thank you - I've only just come back home after being out for several hours:

[pennyannie in reply to Bluesadawg]

I've been beaten to answering you - but ditto the content sent :

Whether hyper or hypo these critical physical symptoms can help people understand better what is happening within their bodies and facts - and which should be used in conjunction with blood test results which are just a snapshot in time and tend to run behind symptoms being experienced.

[Jo5454 in reply to Sleepman]

Can I ask about being a good convertor please? Are there tests for this or is it a case of good levels of T4 to T3? Thank you...

[Sleepman in reply to Jo5454]

Just your T3 and T4 results. T4 a bit more percent through range than T3. 70/60 or 80/70 type numbers the wise ones on here are good.

If your T4 is 100% and T3 at 10% your not converting.

How you feel is more important than numbers, glad you are progressing.

I remember being desperate to be well again.

There is a genetic test too for T3 conversion but if your blood levels are bad then it just conforms that you are more likely to be a bad converter. It is not a yes no indicator.

T3 that is measured is not in your cells though. It is all a bit subtle.

Better if your are not autoimmune type I think in terms of chances of not converting well and less likely to have to avoid gluten and even lactose ....

[Agitator23 in reply to Sleepman]

Actually, I lucked out - have both primary autoimmune thyroiditis and central hypothyroidism 😕 Thanks for that explanation.

[Jo5454 in reply to Sleepman]

Thank you Sleepman for your response, I'm following thus thread and have been wondering about the converting side of things!I'm sorting b12, ferritin, vit d issues at mo but thyroid results have been up.& down in past and currently Ft4 29% through range, FT3 37.i% through range, TSH 2.4, whereas its been 3-4ish last couple yrs. Never taken any thyroid meds, but am going to discuss with Dr at nxt apptmt. Ran out of time in recent apptmt trying to sort b12/ferritin side of things!

Apologies for delayed thanks...

[HealthStarDust]

The long and short of it is, neither are wrong and neither are right. The numbers have their limitations so you need to be guided by a series of consecutive tests and symptoms as far as possible.

Other than that, consider them a round about figure and a snapshot in time.

Honestly, as I’ve learned, it’s not worth a second thought. When you need to be certain in order to change treatment, have multiple tests from different laboratories.

At this stage as you have only been on levothyroxine for 5 weeks, those results are almost meaningless.

[Agitator23 in reply to HealthStarDust]

Thanks. I'm going to stick with 100 mcg for longer and seeing what happens. So, maybe the appointment after next make a decision. My main problem is that my GP is working on a range that's not going to work for me. I'm going to be in a constant loop of saying I'm fine when they test my bloods and use 9 - 19.1.

[HealthStarDust]

PRIVATE fasting 12pm. 3/09/24

TSH 0.046 0.4 - 4.05 minus 9.7%

Free T4 16 10-28 33.3%

Free T3 5.4 3.5-9.46 31.9%

P.S. as others have mentioned, I am not sure I can trust your private test results. Those FT4 and FT3 reference interval seems too wide.

I don’t know the exact way to calculate it, but I suspect if you used the same width? (Is that the word)? Your results would look similar.

[Agitator23 in reply to HealthStarDust]

Yes, I'm taking 28 as too high as top of range for FT4. I'm going with 9 - 24, which used to be the NHS range until relatively recently. Not sure why, who or when that changed.... That makes me 46.7% through range.

[waveylines in reply to Agitator23]

The NHS top of the ranges have been dropping steadily over the years. Years ago it was 27 for top of ft4 range. In my area it's now 21.7!! Who knows what the thinking is and whether the tests have altered to that degree.....it does mean though you will get less treatment to avoid going over the range. Maybe the population ranges has more untreated hypothyroidism given TSH has to be over 10 these days.

[Agitator23 in reply to waveylines]

It's definitely been a trend to decrease upper levels of fT4 range. The reasoning behind it appears to be opaque and has probably led to many more people being untreated or undertreated. There is a big chasm between private sector and NHS diagnosis and treatment. Why? 🤔

[tattybogle in reply to Agitator23]

Big changes in range used at a particular lab are probably due to that lab buying a new test platform . You can see the 'factory setting' for some of the machines currently in use here : healthunlocked.com/thyroidu....

smaller adjustments in range used are probably due to some voodoo combination of : 1) comparison with local population results. (which could be well screened patients with normal thyroid tests , or few passing lab staff .. good luck with getting to the bottom of that one .

2) lab consulting with /taking opinions of local endo's into account ..... (probably the sort of conversations that are not likely to be written down )

[Agitator23 in reply to tattybogle]

All very transparent and scientific, I'm sure 🙄

[waveylines in reply to Agitator23]

Just remember numbers are just that numbers. One day the medical profession will wake up to that fact. That and we are not all the same!! Mutiple factors are at play, something else thats often not considered. X maybe be great for Jill but the same x is pants for Jane. The idea of managing patients through computer figures has been to the detriment of good doctoring sadly. Even worse is the demise of consulting and discussing with patients alongside listening skills. Most of which has been thrown out the window. Doctors are laying themselves wide open to AI taking over.

[tattybogle]

yes extremely unsatisfactory that endo's / labs haven't yet got their act together to insist on sorting out this clusterf*ck.

some stuff i collected here :

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

I recently had quite different fT4 results from GP, and MonitorMyHealth. I did side by side comparison as i have suspected for a long time that my GP results are tending to exaggerate my %'s when fT4 results are near the top end.

GP : (veinous draw~ NHS hospital lab @Lancaster)

TSH 2.65 [0.57 -3.6]

fT4 15.7 [7.9-14] 128% which is over range enough for GP to consider reducing dose.

MonitorMyHealth : (fingerprick ~ NHS hospital lab @Exeter)

TSH 2.9 [0.27 -4.2]

fT4 22.1 [12-22] 101% ... dose is quite likely to be left as is.

The blood samples were taken just 45 minutes apart (same day).

(however , unless we are comparing results taken from the same blood draw , we don't really have much of a leg to stand on when complaining about it , as it is perfectly possible that that the fT4 levels were indeed different )

[Agitator23 in reply to tattybogle]

Wow! These ranges and the TFT interpretations from them are really all over the place. My background is in science and laboratory work and I can't believe how unscientific it is. It really rankles. And it's affecting people's lives each and every day.

I want to know who decides the range and why they're always changing these ranges. It is interesting that the NHS seems always to flag fT4 too high through range and wants to decrease dose and not vice versa occasionally. (Unless others know otherwise). Just wondering why that is....

[Dandelions in reply to Agitator23]

Really interesting. Do let us know more if you find anything out.

[waveylines in reply to tattybogle]

The top of the range on the nhs ft4 is very low as is the bottom Tattybogle. Not seen it as low as that. Monitor my health is also a nhs lab.... their range is like thr range in my area except they're in the south and I'm in the north.

[tattybogle in reply to waveylines]

yes the 7.9-14 range is both low and narrow. Lancaster NHS hospital lab have used this range since 2018, and from posts on here it looks like Bristol NHS hospital lab have been using one very similar for few yrs too , and possible one other area but have forgotten where.

These labs are probably using Beckman-Coulter test machines i think ~you can often tell which test machine they are using by the range used, because different manufactures set the 'factory setting' ranges for their machines , which may then be adjusted very slightly by local area lab ). Diogenes once told me he thought such a low and narrow range was ' rubbish'.

yes, am aware MMH is actually done at Exeter NHS lab , that 's why i use them , in case i ever want to have a conversation with GP about the comparison, hard to get a way with saying they are unreliable if they are from NHS lab.

[waveylines in reply to tattybogle]

That's why I use them too! Not that my GP will enter the results onto my record.....namely cos I paid for them! All a bit mad as I can get my ft4 & ft3 done....doctors are only allowed TSH.

[PamyWamyFamy]

This happened to me recently. My GP called me in for a word when my T4 was apparently < 6.0 but I’d had Randox & Monitor My Health done either side of the NHS blood test. When I showed her my private blood tests she started questioning their accuracy and so I got the MHS result out that showed the tagline “run by the NHS”. She then changed the subject. I know what I think but not sure if I can speculate here……

My T4 actually measured 16.2 both times by two different labs and I’m on both T4 & T3