Pernicious Anaemia Society

Serum v active b12 confusion

Serum v active b12 confusion


I'm finding it difficult to see what low serum but "Normal" active b12 really means.

I'm due back at the doctors to state my case for treatment but read on certain sites that an active b12 above 50 requires no treatment.

Why would serum be low (153pg/ml) but active be normal (67.8pmol/l).

My symptoms are pretty much text book b12 deficiency but I do appreciate that lots of other things cause similar symptoms.

I've had some great help on here but this is the one thing I can't seem to get a grasp of.

I had a low b12 serum test in 2012 (146) but no follow up or active test at the time because a second test came back as 287 because i'd started to self treat with sublingual b12 without realising it effects results. (I stopped it after being told the second test was normal).

Why would serum be low but active be considered normal?

You can see a more detailed account of my history and results on my previous post.

Ps those results are from the end of October and I've been using sublingual methyl b12 since the first week in November.

22 Replies

serum B12 looks at all of the B12 that is in your blood

to get transported to cells B12 needs to be combined with another protein to make 'active' B12 (holotranscobalamin/holoT) which is what the active B12 measures.

Both tests tell you what is going on in the blood but this isn't the whole story and they don't say what is actually happening at the cell level.

Whilst in general low serum and low active B12 will go together and high serum and high active B12 will go together it isn't always the case.


Thanks for the reply. So does that mean that the Gp should still be prescribing b12 to treat the symptoms.

The last one I saw drew a line under the active result and handed the report back to be and told me to eat more fruit and veg.

Meanwhile my feet and legs tingle and my right thigh burns like sunburn. I'm tired like it's going out of fashion, short of breath and the sun, light bulbs and the tv glare me. I've had tinnitus for a long time too.

I'm trying to put together a case for injections on the 5th of Jan but just keep getting dismissed when I beg for treatment.

I sure I should of had treatment in 2012 when my fatigue gets bad but that's so long ago and I made the mistake of supplementing for a week inbetween the two tests for serum b12 so it's pointless arguing about it.

I'm wanting (like most people) evidence/proof to put under the gp's nose to get a trial of b12 injuctions. Sadly their own serum test done days after mine came back as 312 so they just keep quoting that and ignore the other low test results from 2012 and October.


if your GP told you to eat more fruit and veg to deal with a B12 problem then he really was a bit of a chocolate teapot - totally out of his depth on B12 as you need animal products to get B12 - fruit and veg will do nothing unless they have a heavy helping of organic matter on them and you haven't washed them.

as fbirder says - next step would be MMA and homocysteine which would give you some input on what is actually happening at the cell level - they are two waste products that will build up if your body doesn't have enough B12 but can be raised by other things (eg folate being low in the case of homocysteine).


Well, it's often mentioned in here that the serum B12 test is notoriously unreliable and inaccurate. The Active B12 test is, however, often touted as being much more accurate.

So it could be that your serum B12 result is falsely low. Or it could be that you do have a lower ratio of haptocorrin (the protein that binds B12 to form 'inactive' B12) to transcobalamin (that forms active B12). Either way it suggests that your symptoms aren't B12 related.

Ask for a MMA (methylmalonic acid) or hCys (homocysteine) test. They will give a much better idea as to whether your cells are getting enough B12.

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Thanks. It seems like supplementing is my nemesis.

In 2012 I took b12 after the initial low result and it put the Gp off the scent when the repeat test came back ok (287).

I've had four years of fatigue and brain fog and multiple trips to the gp but things got really bad in July when it got my eyes then in August it crippled me and made my heart race every time I stood up. Then I got terrible anxiety.

I've been using methyl b12 since November and despite still feeling rotten I have my sanity back and my eyes aren't as bad.

I'm reluctant to stop the b12 spray in fear of worsening of my symptoms but I don't seem to be feeling any repair as such.

I'm between a rock and a hard place as I'm reading that you need to stop supplementing to get a proper test but I darent stop incase I get really bad again.


Well that's thrown a spanner in my works. I just re read your reply .

You say my symptoms aren't b12 related??

On my previous post people were sure it was a b12 issue.


No, I didn't say that your symptoms aren't B12 related. I said that the high active B12 suggests that they aren't. And your doctor obviously reckons that they aren't.

On your serum B12 alone it does look like a B12 deficiency. But the active test result argues against that.

However, if you were supplementing in the months before the active test then it could well be meaningless as it would increase the levels.

For the MMA and/or hCys tests to give a reliable result you'd have to stop supplementing.

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I'm waiting on the results of a spine MRI.

If that comes back ok I may stop all supplements and see if I can ride it out long enough to get accurate test results.


Here's a link to my blood results from 2012 and the most recent ones.

They didn't test b12 again after the repeat 2012 test until I did a private test in October 2016 and took the results in.

Maybe you could take a look and offer an opinion. (I got very useful feedback on a previous post but I'm interest in other people opinions who also have a good understanding of the issues).


So, serum B12 was low in Jul 2012 and Oct 2016 but OK in Nov 2016.

Active B12 was normal in Nov 2016.

You're supplementing with B12 spray, but it doesn't seem to be improving your symptoms.

I would follow one of two routes -

Stop the supplements for three months if you can get the doc to agree to tests for serum B12, Active B12, MMA and hCys - or as many as possible (at least serum B12 and MMA) after your dry-out.


Start self-injecting and see if that fixes your symptoms. If it does then tell the doc and see if that changes their mind (some seem to think it's worth giving you the jabs to stop the 'danger' of your self-injecting).


I do feel better on the b12.

Before I started it I'd gotten very poorly. My wife and I were discussing what's posted above and she says I'm massively improved since I started methyl b12, D3, gentle Iron, multi vitamin spray, magnesium & calcium 2:1.

This is both a minefield and a nightmare because I don't feel well but don't know how to fix it.

The timescales re testing are so long too especially when you factor in the worry of permanent nerve damage.

I only started having what I'd deem bad neurological problems in July with light glare then burning skin on my thigh and ocular migrane and postural tachycardia in august although I guess they've been around for a long time in a milder way but I was living ok with them and able to go to work etc.


I did use a multivitamin spray in May, June up to the end of July but stopped it as I began to feel worse with light glare etc.

I'd been off it for pretty much three months when I did my private b12 test.

It only contained 6ug of b12 though and I'd not been eating fortified cereals etc with being dairy intolerant.

I'm not a massive meat eater but I do eat it.

I've recently tried gluten free cereals etc and find it improved my stomach discomfort and constipation a lot. I however tested negative for celiac and my intrinsic factor and PA came back as ok. All the autoimmune tests they did came back negative.

I did a private hpylori stool antigen test last month and that came back negative thankfully. I got stomach pains again about a year ago but used mastic gum and that resolved things nicely.


My personal view, I am not a medic , is that none of the tests linked to B12 issues eg serum b12, active b12, MMA, Homocysteine , intrinsic factor antibodies are foolproof.

Most of my results over the years have come back negative/normal range while I continued to deteriorate with symptoms that were typical of b12 deficiency. I only improved when I started to self treat as i was unable at that point to get NHS B12 treatment.

I wasted money on private tests a few years ago. I was supplementing at the time with b12 and I queried whether this would affect the validity of results but got a very vague answer so went ahead with tests only for them all to come back normal range.

Can't remember where you live Steap. Is it UK?

It is made clear in the BSH Cobalamin and Folate Guidelines, a UK B12 document, that people who are symptomatic for B12 deficiency should be treated even if serum b12 is normal range. click on box that says "Diagnosis of b12 and Folate deficiency" shoudl be on page 3 or put "cobalamin and folate guidelines" in search box.

link to flowchart in BSH cobalamin Guidelines


Yes! I agree with you, Sleepybunny!🐇


Yes sleepy bunny I'm in the uk,

I got hydroxycobalamin 1mg/ml vials from a German pharmacy before xmas but my needle packs got lost in the post so I'm still waiting on the re sent ones.

I'm very reluctant to self inject though. (That purchase was my last resort/plan z)

I'd much prefer to get proper treatment and to be monitored by my gp. Especially with the albeit small risk of a reaction.

I get hives from fresh air some days lol.

Lots of things get me like milk, some fats, bread, McDonald's fries, pollen, animals etc etc

Ps I'm a registered nurse so ok with self injecting if I need to.


Hi Steap,

I think I'd go with fbirder's suggestion to self inject B12. It would most likely make more of your symptoms go away and you would feel so much better, if it is low B12, which is what it sounds like to me. And as he points out, the doctor might offer B12 injections to you!

I am not a medic but I know when my B12 was 290 (range: 200-1000, sorry can't remember units of measurement) I had lots of neuro symptoms and was super fatigued.

If you decide to self inject, post again asking for info on where to buy it. I'm in the US so I can't be of much help on that topic.

I get a prescription for methyl from a Naturopathic doctor and my husband injects me. I feel a million times better.☺ The last tenacious symptom is tinnitus, but that is very slowly getting better as well.

My regular GP put me on cyanocobalamin, which unfortunately did not work for me. No change in symptoms after a year of once a month shots. It only raised my serum levels to 600, up from 290, which I've always thought should have be higher after a year of shots.

I also, like you, take gentle iron, sublingual D3 drops, a multi vitamin. And I take sublingual methylfolate, 400 mcgs.

I'm assuming you are in the U.K. and can get hydroxocobalamin from Germany, I believe, which breaks down into methyl and adenosylcobalamin in the body.

The good thing about self injecting is that you can self inject whenever you feel the need. No chance of overdose on B12 since it is water soluble- there is lots of documentation on that subject.

I feel the need to inject every other day and sometimes my tinnitus is gone for days. 😊

It also feels great not to have to depend on a GP to tell me how often I can have B12, since most of them are appallingly ignorant when it cones to B12.

☺Best of luck with it all! 💉💉


Thank you.

I was going down that route and hoping my Gp would prescribe the loading doses and monitor me but got a bit thrown there with the comment about the active b12 suggesting my issues are not b12.

I'd been going with the theory that it's been low since before 2012 when I get a pre supplements result of 146 pg but they ignored it. I've had rotten fatigue since before then but things ramp up loads from July this year. Then gets terrible in august after I try to push my self exercising.

I do feel better on the oral methyl b12 and still don't know conclusively if my blood count is significant as different people say different things.

I've posted a link to my results from 2012 and this year above.

Sadly I supplemented with high dose b12 before the repeated test in 2012 because I didn't know it effected results and no one told me or asked at the doctors surgery. I think that decision changed my life massively as I stopped right after being told my levels were actually ok.

They never considered b12 as an issue despite my repeated visits to complain about fatigue and brain fog.

I did a private active test in October after the Gp refused to give me "my most recent b12 results" when I asked for them when he was prescribing antidepressants and referring me for cbt for anxiety.

I wrongly presumed they would of been keeping an eye on my b12 with all my complaining of fatigue. How wrong I was.

He did do a test when I showed him my results but that came back as 314pg and he refused treatment or further tests despite my own serum results only a few days earlier being 153pg.

FYI my vitamin d was 49 which I'm led to believe is one point under normal. My fatigue nurse showed me the report on her computer and the lab report said *low but the Gp had commented on it with "no further action required".

I had a confirmed hpylori infection in 2012 and they diagnose a duodenal ulcer and treated it with ten days of antibiotics. I'd had IBS for years prior to that.

For the last few years I've had a lot of constipation and little but I guess now significant neurological symptoms like electric shocks running along my spine and laying in bed and not knowing where my arms were unless I moved them. I'd not realised what that meant until recently when I looked at symptom checklists on the b12 sites.

I'm still at a massive loss though with the confusion over the serum and active b12 results.

I wish we had a haematology specialist on here.


Oh, gosh, how frustrating for you! I agree with Sleepybunny that its best to treat symptoms and not worry about the B12 levels.

I don't know what my levels are now and don't care because I know how much better I feel when I inject every 2 days. But I am lucky in that the naturopath I see is fully conversant with all things B12. I feel so fortunate that I can have all the B12 I need. I seem to need a lot!

I would try to get treated based on your symptoms. There is a very good book 'Could it be B12?' by Sally Pacholok. She recommends keeping B12 levels high as neuro symptoms can present even with levels in the 500's and under. In Germany and Japan folks get treated if their levels are below 500.

Imho, if you could focus on your symptoms and try not to even think about what your B12 levels are, you could avoid worry and get on with it. :)

If I had to go through the frustration of trying to get a conventional doctor to understand and treat me, I'd be a very sick and very frustrated puppy indeed.

I can't stress enough how it is the symptoms that are the more important issue here!

Keep us posted and I wish you well!


I bought Sally's book last month.

It's very interesting.

I considered buying a few copies and donating them to my Gp surgery.

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Good idea! ☺


Hi Steap,

I gave a copy of Martyn Hooper's book "What You Need to Know About Pernicious Anaemia and Vitamin B12 Deficiency" to my GPs.

"after the Gp refused to give me "my most recent b12 results" when I asked for them "

I have read that GPs may refuse to give results if they feel that giving the results could harm the patient in some way. Did they explain exactly why they refused?

Perhaps a few months later, they may now be willing to give you these results?


I'd did the typical Gp surgery thing and asked right at the end of the consultantion. He simply said "no because I've logged out now".

I did get them all from the receptionist at my next visit.

They're not bad GP's but I know they too are over worked and over stressed. It's no wonder considering they only get about five minutes per patient.

He wouldn't of been able to oblige anyway as they hadn't checked my b12 since 2012 unbeknown to me.

I'd presumed they'd be keeping an eye on things like that as I'd even been referred to a chronic fatigue clinic after they'd 'excluded everything'.


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