Once I start supplementing B12, will my B12 blood tests still be accurate?

[Carrie234]

I would like to know if blood tests will still be a useful measure of my B12 levels, once I have started supplementing B12. I would be testing active B12.

The reason I ask is that I have read pernicious anemia people saying that once they start injections (and supplements too maybe), that the B12 blood test result is meaningless - that it will be high but that doesn't mean the B12 is getting to the cells and it doesn't mean that injections should be stopped.

In my case I am going to start supplementing by swallowing a pill along with food, if that's relevant.

[CoeliacMum1]

Yes heard the same and I can see both sides of situation.

I have pernicious anaemia and on 3month injections via GP and my B12 gets tested annually with many other tests for my long term autoimmune conditions… it is possibly it’s for more my coeliacs situation so they test it for as my gastroenterologist stated he wanted it testing as I was extremely deficient in many things and supplement with various things at times and it still was showing dips at times, so they continued to test mine … I just try to time my test right before my next B12 injection but doesn’t always fall right so then obviously it’s extremely high.

But mostly it doesn’t get tested, I have found they expect you to be ok …I see no harm in annual tests it picks up if it drops significantly which mine did in my early years of being coeliac and diagnosis of pernicious anaemia.

Just a couple of years ago I had dip in my vitamin D I supplemented on 3000 units a day but it obviously wasn’t enough if I didn’t get this tested I would’ve thought I was ok on that amount but use 4000 all year round now and my levels were good this year… I can’t say it works for other vitamins as B12 is intramuscular and my issues with absorption might be digestive regardless my B12 went down by 400 once and another time dropped again from previous years it wasn’t deficient but drastic change, can’t say it’s happening now … I also know if I miss 2 injections I’m in deficient range as due to testing one newbie GP cancelled my prescription for them as my range was high, I had a check up with gastroenterologist later that year and he tested it and deficient and it’s how my letter ended up stating these being done annually.

I look at this TSH malarkey being similar, they are giving you a drug to alter test results, medicating a result, but it’s not stating the state of thyroid hormones or symptoms it’s only part of the issue. So the total B12 test gives overall in body, the active B12, shows what is available for body to use, but are we using it well 🤷🏻‍♀️

[Carrie234 in reply to CoeliacMum1]

thank you CoeliacMum1! Yes I agree about TSH and medicating a result

[helvella Administrator Thyroid UK]

If you are taking B12 then you can expect the B12 level to rise in any test - active or standard serum.

If you don't test, you cannot prove you are absorbing a significant amount.

If you are absorbing reasonably, then the test result will be higher for a long time after taking the B12. Which rather undermines any interpretation.

If you are not absorbing, and blood level has not risen as expected, then this would be the point at which you need to get a diagnosis - for example, of Pernicious Anaemia.

Remember that with injections, the level quickly rises and will probably be above the highest the lab can measure. (Labs typically record >2000 - or similar. Meaning you are past the top of their reference interval and they see no point in going through extra processes to get a true reading of, say, 3000 or 4000.)

[Carrie234]

Thanks helvella!

So if I am absorbing because my B12 blood tests are higher after taking an oral B12 supplement which I swallow, then how can I know if it's reaching my cells or not? Can I still be functionally deficient even if my blood levels are high?