Why are blood tests unreliable once i... - Pernicious Anaemi...

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Why are blood tests unreliable once injections have started?


Since I started b12 injections at the end of last year, blood tests show really high levels - nearly 1000. So, when I go to my doctor and try to explain why I feel some recent neuro symptoms are connected to B12 and probably indicate Pernicious Anaemia, he closes me down reasoning that I am clearly not deficient. I have heard from this forum that bloods post-injections are meaningless. Why is this? And how can I break this down for my GP so that he will understand?

9 Replies


In the summary of b12 documents in third pinned post (last link in list) there is a section about Further Testing of B12 being unnecessary.


a) serum B12 tells you how much B12 you have in your blood.

Serum B12 isn't used by your blood it is used by processes that run in your cells.

Serum B12 tells you nothing about what is happening with those processes

b) serum B12 is a potentially useful test for identifying an absorption problem because it provides a measure of whether you are managing to maintain B12 levels in your blood from your diet/stores in your liver

c) if you have had injections you have put a load of B12 into your cells and all the serum B12 test is telling you at this point is how quickly that B12 is being removed by your kidneys.

d) significant numbers of people respond to high serum B12 by making the mechanism that allows B12 to pass from blood to cells a lot less efficient. This is common enough for symptoms of B12 deficiency with raised serum B12 to be recognised as an early warning of some conditions (kidney and liver problems) that lead to raised serum B12 levels.

So, if you have artificially raised your patients B12 levels by giving them an injection, it shouldn't come as a surprise that significant numbers of your patients would have this reaction - leading to functional B12 deficiency

e) Serum B12 isn't toxic so it is possible to treat the reaction by keeping serum B12 levels high enough to ensure that enough manages to trickle into cells - like building a dam and then keeping waterlevels high so enough trickles over the top.

f) So, if your patient is one of the group that responds to raised serum B12 by not allowing B12 to get from cell to blood so efficiently they are going to need much higher levels of B12.

Basically normal range does not apply after B12 shots because some of the fundamental parameters involved in determining the normal range have been fundamentally changed.

fbirder in reply to Gambit62

If Benji76 is going to pass this info on to a doctor I think you might need a reference to back up point d). Especially the ‘significant numbers’ bit. Otherwise the doctor is going to say that they’d never heard of it and, when got told it was from the Internet, dismiss it out of hand.

Gambit based on this are you saying that having injections that raise your B12 levels to high ranges can actually cause a functional B12 deficiency? If that’s the cause I think the advocation of B12 injections immediately following tests showing low B12 serum levels should be reconsidered. Especially if the cause of the deficiency is undetermined. Do you agree? If the deficiency is dietary you could be unnecessarily subjecting someone to a lifetime of B12 injections for no reason

Gambit62Administrator in reply to elvistoronto1

ditto for someone who is supplementing with high dose tablets but doesn't need to. It isn't as risk free as people think.

Treatment should never be based on serum B12 anyway. More useful to see falling levels over time to confirm an absorption problem but test isn't routine so that doesn't happen.

However, can isn't the same as will. It isn't clear what causes the reaction (probably genetic but what gene's etc ....). Will be interesting to see what comes out of the latest PAS research on why some people need much more frequent injections.

Wow. Have to say I'm kind of shocked to learn that - given how much emphasis is put on pushing doctors to provide more frequent shots by many of the people on this forum. Given that many of the tests for B12 deficiency causes are inconclusive it almost seems like a "damned if you do - damned if you don't" type scenario. I was put on shots by my doctor right away with a level of 153 p/mol without investigation into the cause of my deficiency. She just wanted the levels up right away. It would be disappointed to learn that I will have to continue this for life because now my levels are greatly above reference ranges.

And the comment about "not as risk free as people think" needs to be communicated more to everyone here. It obviously contradicts the common opinion here (which is also commonly a point made to doctors) that B12 is a harmless vitamin that is simply excreted when we have more than we need. I guess the key is to find out the cause of the deficiency before any supplementation takes place.

Gambit62Administrator in reply to elvistoronto1

would be good if you could find out the cause but many of the tests aimed at finding the cause of a B12 deficiency can be inconclusive - particularly those related to PA itself.

On one level B12 is a harmless vitamin - it isn't toxic - and it's also quite cheap - but an untreated deficiency will definitely kill you. The sad thing is that GPs don't recognise that B12 really isn't a one size fits all thing and that some people do need B12 much more frequently than others post loading shots.

The latest BMJ research document summary below demonstrates the uselessness of testing after treatment as do other guidelines so, hopefully GP will probably be able to access and read the full BMJ document (behind a paywall) .

At the bottom of page 4 ' under, 'How is Response to treatment assessed'), it outlines that, once treatment is given, blood levels will inevitably increase but it is the clinical condition of the patient that is important:

"Cobalamin and holotranscobalamin levels are not helpful because they increase with vitamin B12 influx regardless of the effectiveness of treatment, and retesting is not usually required."


This Dutch link re. Misconceptions about B12" - No. 5 refers to this too:


Good luck Benji - it may be more effective to put the above in writing so it is on record.

Brilliant. Thanks everyone.

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