Vitamin B12 and blood tests : On reading various... - Thyroid UK

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Vitamin B12 and blood tests

Caroline888
Caroline888

On reading various posts, I have often come across the warning that supplementing with B12 prior to testing can skew blood test results. I don't understand what this means and why it is important. I would be grateful if some knowledgeable member could explain.

I am a vegetarian and I do supplement and my B12 is slightly above range at the moment.

Any advice would be appreciated.

Best wishes

Caroline

37 Replies
SeasideSusie
SeasideSusieAdministrator

Caroline888

It's Biotin, B7, contained in a B Complex or taken as a stand alone supplement, that skews results. This is because biotin is used in some assays. So it's advised to leave off Biotin or B Complex containing it for 3-5 days before any blood tests.

When testing B12, to get a true baseline to see what you are holding onto then B12 supplement needs to be left off for 4-5 months. Testing whilst supplementing shows whether the dose you are taking is enough, too much or too little.

As you supplement B12, are you also taking a B Complex which is needed to balance all the B vitamins? An over range B12 when supplementing isn't a problem, excess B12 is excreted, the only thing is that it's wasting money. When mine showed over range I just reduced the number of days per week that I took my B12 supplement and that now maintains it at the top of the range.

Thanks Susie. I do understand about biotin since it has been explained on this site many times (mostly by you!) about not taking it before thyroid function blood tests.

Yes I am taking a B complex too. I think I understand now: you need to test B12 before even starting to take a B12 supplement if you want to get a true picture of your B12 level. Is there an advantage, then, in having a true baseline? Why does it matter if you are taking enough B12 as a supplement?

Sorry if I seem a bit obtuse but am struggling to understand.

Thanks for taking the time to reply.

Best wishes

Caroline

SeasideSusie
SeasideSusieAdministrator in reply to Caroline888

Caroline

Testing before supplementing will tell you your baseline (for any vitamin/mineral) and indictate whether you need to supplement or not.

"Why does it matter if you are taking enough B12 as a supplement?"

I'm not sure what you mean. If you are low when tested then you need to take a certain dose to raise your level. If you don't take enough it won't raise your level sufficiently.

SeasideSusie

Can't you just jump straight to supplements without knowing your true level (which, I suppose, is what I did, as I was never told I was deficient). Being a vegetarian I just assumed it would be wise.

I was just curious about the regular references to supplementing with B12 skewing B12 test results, but I think I understand now that you are saying that with supplementation the result of a B12 blood test will inevitably be affected by the supplement. Perhaps in the same way as taking T4 before thyroid function tests affects the level of T4 in the blood.I

I think I understand now. Thank you😊

SeasideSusie
SeasideSusieAdministrator in reply to Caroline888

Caroline

Can't you just jump straight to supplements without knowing your true level

But why would you?

You need to know if you need to supplement. If your levels are good, why supplement and waste money?

Some vitamins are water soluble and any excess is excreted - B vitamins, Vit C.

Some are fat soluble and can't be excreted so they are stored - Vits A, K, E, D. Taking these when you already have a good level means you will eventually reach toxicity level.

Supplementing iron when your ferritin and serum iron levels are already good again causes problems, you'll get iron overload and that will lead to problems.

I only meant a B12 supplement, which I was told at a Vegetarian Society meeting over forty years ago was something to consider if dairy produce was not a reasonable part of my diet. I don't like eggs or milk so, as I've got older, a B12 supplement plus B complex seemed a good idea.

I was tested and found to be severely deficient in vitamin D so take 2000i.u. daily as recommended by a consultant at the Queens Medical Centre. Obviously I take vitamin k and magnesium along with vitamin D.

I would never take iron supplements without proper advice. As you know, I have just sent for an iron deficiency test from Medichecks.

Sorry, I misled you into thinking I would supplement willy-nilly.

I am grateful for all your advice as always.

Best wishes

Caroline

SeasideSusie
SeasideSusieAdministrator in reply to Caroline888

Caroline

Was 2000iu D3 the prescribed amount for your severe deficiency? Or did you have loading doses? What was your actual level when diagnosed?

Initially I was told by the consultant to take 2000 i.U. daily for a fortnight, then 1000 i.U. for 3 months before being retested. My initial blood test showed a level of 11 nmol which was classed as severely deficient. I was surprised that I wasn't prescribed a much higher dose as I had seen very high doses (loading doses) mentioned online. Anyway I did as he said and my level went up to 83 nmol! He was very surprised but put it down to the fact that I have a low BMI.

I carried on taking 1000 i.U. for a year or two until my GP phoned at the end of one summer to say my level had gone down instead of up as would be expected and to up my dose. Subsequent tests have always shown results around the 100 nmol mark. The last one in November last year was 108 nmol.

SeasideSusie
SeasideSusieAdministrator in reply to Caroline888

My initial blood test showed a level of 11 nmol which was classed as severely deficient. I was surprised that I wasn't prescribed a much higher dose as I had seen very high doses (loading doses) mentioned online. Anyway I did as he said and my level went up to 83 nmol!

I'm amazed!

I was too😊

shaws
shawsAdministrator in reply to Caroline888

Also both Vit B12 and Vit D are prohormones rather than vitamins and both have to be optimum. Listen to this from the P.A. Conference and most important is around 4 minutes in a talk by a Professor re B12/Alzeimers.

youtube.com/watch?v=n7aMPF5...

Caroline888
Caroline888 in reply to shaws

Thank you shaws, just watched the above. It was very enlightening! Interestingly, my mother was diagnosed with dementia about twenty years ago and advised at the Memory Clinic to take vitamin B12 for her memory issues. She survived quite comfortably for eighteen years, with the diagnosis only becoming much more apparent during the last five years of her life. The nurse helping with her care at the end was amazed she had lived for 18 years with dementia and said that a five-year life expectancy following diagnosis was far more usual.

We gave mum vitamin B12 as instructed. It looks as if the knowledge or suspicion that B12 could help prevent progression of the disease was there even then!

Thank you for the link.

Best wishes

Caroline

shaws
shawsAdministrator in reply to Caroline888

My mother had P.A. as I do as well. She got the regular B12 injections.

Long before I was diagnosed the doctor told my mother she need no more B12 injections as her bloods were 'fine. Both my sister and I thought that was good news. Not so as my mother died an awful death through stomach cancer which can be caused by neglected P.A. I didn't find this information until long afterwards.

washingtonpost.com/archive/...

nightingale-56

nightingale-56
nightingale-56 in reply to shaws

shaws thank you for drawing my attention ot this post. It will be most useful to show my son's carers, also Social Worker as we are to have a Review in a few weeks time.

Caroline888
Caroline888 in reply to shaws

Am so sorry to hear that. It just underlines the fact that we have to take everything doctors say with a little scepticism and check for ourselves. Disgraceful really.

Hope you are keeping well.

Best wishes

Caroline

shaws
shawsAdministrator in reply to Caroline888

Thankfully, I am well and that's down to a doctor who was troubled by my blood test about thirty years ago and I said my mother had P.A. I then had an 'intrinsic factor test' I don't think they do it these days which confirmed P.A. so had no symptoms at that time or have developed any so far.

Caroline888
Caroline888 in reply to shaws

That’s so good. Hope you continue to feel well!

The thing about not having a base-line for B12 is that you might have Pernicious Anemia but you won't see your B12 is that low if you start supplementing before you get tested. :)

Thanks greygoose. It's all very complicated isn't it? Presumably you could develop pernicious anaemia after you have been supplementing with B12 for a long time and the supplementation would mask the fact.

You could have had it before you started supplementing, come to that. :)

So true!

The serum blood test tells you the amount of B12 circulating in the blood. So if you are supplementing - the result will be high. However B12 is needed in the cells where it is utilised and only around 20% of your result is able to be transported to the cells.

Caroline888
Caroline888 in reply to Marz

So does that mean that even if your blood test shows a high level of B12, you could still be deficient? As you can see, I am a bit confused!

Marz
Marz in reply to Caroline888

Not deficient in the blood - but could be low in the cells. If Homocysteine and MMA are raised then that can indicate low levels of B12 in the cells ..

Caroline888
Caroline888 in reply to Marz

Thank you Marz

I've been wondering about this for a while, so thank you for explaining it to me.

Best wishes

Caroline

Marz
Marz in reply to Caroline888

biolab.co.uk/docs/vitaminB1...

Am wondering if the above is helpful ? Found it stored away in my Health File :-)

Caroline888
Caroline888 in reply to Marz

Thank you Marz, very interesting article!

Usually the RDA for B12 is said to be 2.5 ug but this article states that we actually only need approximately 1 ug/day which is surprising and makes me think surely I must get that despite my vegetarian diet and the fact that I don't much care for eggs and dislike milk per se. I do eat all kinds of cheese and natural yoghurt.

Of course absorption could be an issue, I wouldn't know.

Apparently B12 deficiency increases the risk of strokes and dementia, both of which figure prominently in my family history.

I read the article with my morning cup of tea, so not at my most alert and it was quite technical, so reading it again would be useful I'm sure!

Thank you for taking the time to look it out for me.

Best wishes

Caroline

Marz
Marz in reply to Caroline888

When B12 is low in the cells - Homocysteine can be raised - it is this marker that can be indicative of heart issues and strokes - sadly. It is rarely tested on the NHS. Once I was aware of it some 13/14 years ago I had it tested here in Crete and as it was raised took action. I could write more but ... :-) Read up on Cholesterol v Homocysteine. The research for the latter was buried in the 60's as Statins were about to be launched ...

Caroline888
Caroline888 in reply to Marz

Thanks Marz. I will do that. My cholesterol was raised last October just prior to starting treatment with levothyroxine. Am hoping that treatment with levo will have lowered it but have not checked yet. I do stay off butter and all margarines, though I am aware that diet does not greatly affect cholesterol levels.

I will look into the homocysteine vs cholesterol connection just to see if I should be doing anything differently. Thank you for your suggestions. Certainly statins are not going to figure in my future!!

Thanks again.

Best wishes

Caroline

Marz
Marz in reply to Caroline888

Sorry think I confused you - when research showed Homocysteine was found in plaque as well as cholesterol - the research was quickly buried. Raised homocysteine is a marker for heart issues and strokes - the cure being B12 and other B vitamins. So they opted for cholesterol and money spinning statins .. 😊 Good fats are good for you ... !

Caroline888
Caroline888 in reply to Marz

Thanks Marz. I am easily confused but will know better when I do the reading you suggested.

I do eat healthy fats such as olive oil and lots of nuts and seeds. I know we need fat, even a certain amount of saturated fat, so I’ve not given it up entirely!

As you can imagine, my GP has twice suggested statins but has not been too pushy when I declined.

Thanks again for your help.

Best wishes

Caroline

Suppose a patient suffers B12 deficiency e.g. a level of 180 with a range of 200 - 700. Without doing any testing they start taking high dose B12 supplements and they take them for 6 months. They aren't able to absorb B12 very well - perhaps because of some gut problem or gastritis, or because they have pernicious anaemia (PA). Their level may rise to 210 with the same range after 6 months. (Which would be a terrible result after 6 months of supplementing!)

There are plenty of doctors in the UK (I'm not sure about other places) that would look at a level of 210 and say it's fine because its in range - take tablets if you want a higher level.

However, if they had ever seen the result of 180 they may have been persuaded to test for PA, and they may also have agreed to loading injections and regular treatment.

To find out a patient's level of B12 before supplementing may require the patient to stay off supplements for several months. And if they are already very low in B12 then several more months without sufficient B12 to find out the baseline level could cause lots of damage.

Goodness, it is so involved! Fortunately I believe I have been tested enough times in the past, prior to supplementing, for PA to have become apparent if it existed. That's assuming the GP concerned at the time knew his stuff!! As we all know, GPs don't always live up to expectation😡.

Thank you so much for your explanation.

Best wishes

Caroline

suggest you take a look through the pinned posts on the PAS forum,

healthunlocked.com/pasoc

particularly this one

b12-institute.nl/caution-no...

If you are taking supplements - particularly high dose B12 supplements - then you are bypassing the normal mechanism that actually regulates how much B12 is absorbed.

Serum B12 is a test that can be useful in identifying an absorption problem as levels will fall if you have an absorption problem because the mechanism that releases your stores depends on the same mechanism that you use to absorb B12, So the test becomes much more difficult to interpret and will more likely than not be mis-interpreted as meaning that you don't have a B12 problem and you are okay..

If your levels are high then I would suggest cutting back on the supplementation. B12 isn't toxic but some people do experience problems with the mechanism that allows B12 to pass from blood to cells if serum B12 is raised.

Caroline888
Caroline888 in reply to Gambit62

Gambit62G

Thank you for all that information.

I do not take a high-dose supplement. My B12 is included in a multivitamin (25 ug) and in a vitamin B complex (30 ug). SeasideSusie disapproves of multivitamins so I am considering dropping the multi and taking just the B complex, but at the moment I am alternating the two until my multivitamins run out.

My level of B12 is slightly above range.

Gambit62
Gambit62 in reply to Caroline888

25ug is quite a high dose if you don't have an absorption problem, so it could result in levels build up over time. RDA for B12 is 2.5ug - in the absence of an absorption problem the body is quite efficient in the way it uses B12.

If you had previous results that showed levels in the normal range then it would suggest that you may not need to supplement B12 at all at the moment, certainly not if you aren't symptomatic.

Personally I'd prefer to be taking supplements separately - some vitamins can cause problems in excess - one I'm really aware of is B6 and using individual supplements gives more flexibility in varying one over another - but I do have absorption problems so the situation is a little difficult.

Caroline888
Caroline888 in reply to Gambit62

Thanks Gambit62

I agree that 25 ug is far more than the recommended RDA. On the bottle of the multi it says it's 1000% of the RDA which I thought seemed excessive until I saw bottles containing 1000 ug of B12 on Amazon.

I will give some serious thought to what you have said. I am a vegetarian which is the main reason I take a multivitamin as some nutrients are difficult to get from a vegetarian diet, B12 in particular. But I plan to cut down a little on the B12 by swapping my multi for a B complex containing 15 ug B12 per tablet.

I agree with you that caution is advisable, especially with B6 which I understand can cause numbness and nerve damage in excess.

Thank you so much for taking the trouble to reply.

Best wishes

Caroline

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