I recently ordered some Medichecks blood tests & paid to have the blood taken at my local NHS hospital. I had to have bloods for my GP at the same time. Several tests crossed over.
I’m really surprised to see the difference.
Example….
B12 :
NHS = 293 ng/L (211-911ng/L) Tell patient OK
Med = 30.9 pmol/L (37.5-150pmol/L) Deficient
Serum Folate :
NHS = 7.8ug/L (>5.40ug/L) Within Normal Limits
Med = 2.95ug/L (>3.9ug/L) Deficient
Quite alarming discrepancies & the difference between getting treatment and not.
Any ideas what’s going on here?
Written by
knackersyard
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medichecks is active B12 and NHS is serum B12. Active B12 measures just the B12 bound to TC2 - the protein that enables it to move into cells.Folate is very responsive to dietary intake as the body doesn't have a store it can use to regulate blood levels but the differences do seem to be somewhat greater than would be expected - particularly if samples were taken at the same time and by the same person
Scientist, not medic. I have wide experience of assessing labs for their performance against agreed standards. You wonder why the discrepancies; I'll open the can of worms. Here we go: [and it'll go on a bit]
The methods for FBC, despite different manufacturers, will typically give very similar results around the country. All respectable analytical labs participate in a National External Quality Assurance Scheme [NEQAS] and can show how they perform against other labs, and perhaps more importantly, against themselves, over time. That's another lecture, I'm afraid!
Eyeballing the FBC results that does seem to be the case; both sets are normal, but if either sample had been repeated on the chosen analyser, I suspect they'd have been closer.
My assumption is that you had the NHS sample taken in an NHS site, and therefore that's likely to have been analysed more promptly than the Medicheks one. I can't see any date evidence of when they were tested so it's only a wild guess. Fresh blood is just that; fresh. It 'goes off' quite quickly, whatever we like to think. Things that can change on storage are the MCV and MCV-linked values; Hct and MCHC. The platelets will inevitably swell on storage, so much so that issuing MPV results is fraught with issues.
For the blood to be analysed, we add an anticoagulant, or it'd be clotted solid within a few minutes. The concentration of anticoagulant is critical. 'more' isn't always 'better' but 'less' is more of a problem. Your FBC blood was taken into two FBC tubes, and dependent on the tube and the amount of blood, and the time to analysis, there's another source of error. The MPV is particularly susceptible.
Folate is labile. If the folate sample isn't treated with the greatest respect then the results may not be too helpful. Plus the methods for folate assay are numerous, and they won't all give the same results on the same samples.
Serum B12 vs Active B12 is even more of a minefield, plus when some labs are reporting in molar concentration and others are using mass units, it's even more confusing.
So, what's going on here? Well, that's a question that could be better posed to the two labortories who analysed the samples; I'm not taking sides in this one...
Also not a scientist, but isn’t it quite possible to appear ‘normal’ on total serum B12, and deficient on active B12, as the ‘total’ figure can mask if the bioavailable amount is low? I think that is why active B12 is suggested as a much better biomarker for deficiency than total B12.
I think it would be worth taking it back to the GP, to show them the deficiency in active B12 from the medichecks results (and the other deficient result) and asking if they can do further tests (eg MMA / homocysteine) to get to the bottom of it. I suspect they are not able to access MMA / homocysteine tests, so if not, might be worth going back to medichecks for MMA / homocysteine tests.. good luck!
Hi. You have a point, and it's a good one. The difference between Total [serum] and Active B12 is simply the ratio of Haptocorrin to Transcobalamin, and we're all different. I wonder if we'll see a more widespread adoption of 'Active' in the future? It was appearing when I retired all those years ago, in 2010. If it really was so much better, then I suspect that the NHS labs would already be adopting it more widely, but we'll see. Often, NHS labs are tied into contracts for methods for several years. It's always worth asking if you don't fully understand something. [It's actually quite good asking when you fully understand stuff too.]
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