Anyone else seem to have some sort of... - Pernicious Anaemi...

Pernicious Anaemia Society
22,828 members16,081 posts

Anyone else seem to have some sort of “triggered” intrinsic factor blocking antibody?


I’m 21 years old, an athlete and up until a couple months ago completely healthy. Then I got mono and 12 weeks later the fatigue had not gone away and the dr found I had a b12 deficiency (135 pg/mL). She then gave me a double dose of B12 shot and then I got blood drawn for an IFBA test. It came back positive. I have never had any issues before and my doctor has been wholly unhelpful (I’ll be seeking another doctor) but I was hoping to get some anecdotal stories from other people to see if they experienced something similar. Thanks!

10 Replies


Having been a runner 🏃🏽‍♀️ for 43 years (I’m trying to continue when I am able), I understand what a shock it can be when extreme fatigue sets in and you just can’t return to normal. Mononucleosis is caused by the Epstein-Barr Virus, which is known to cause a multitude of other ailments. I’m not an expert, nor am I aware of its association specifically to intrinsic factor, but it wouldn’t surprise me.

I never had mono but had a “positive” EBV titre. (I have a long complex medical history if you want to read my posts but I won’t go into that here). I have never had intrinsic factor tested, just told to continue taking sublingual B12 because it works for me. My diagnosis is still being worked up but chronic B12 deficiency is a piece of it.

Hang in there. It does get better! There are some very experienced and knowledgeable people on here. I’m sure they will be of more assistance 😺


Having a positive Intrinsic Factor Blocking Antibody test means that you have Pernicious Anaemia , an autoimmune condition , which could account for your exhaustion. I would think that the occurrence so shortly after a diagnosis of mononucleosis is entirely coincidental . It takes time to develop P.A. so it’s probably been developing over some time . Mononucleosis is linked to other autoimmune conditions , and you rarely have one of them . Most people have 2 or even more . E.g I have P.A. and R.A. ( rheumatoid arthritis )

You should have received loading injections of B12 ( 6 over 2weeks . ) Then an injection every 2 months ( latest guidelines ) . Some people need injections more often than that . It’s to be hoped that your exhaustion will disappear .If not , try to get more regular injections . Best wishes .

Just want to say that it’s quite usual for doctors to have no understanding of Pernicious Anaemia . That’s why the P.A.S. was formed by Martyn Hooper . It’s been invaluable to me .

Also you need to make sure that you get plenty of folate in your diet ( folic acid if in tablet form) Vitamin B9 works together with B12 . I’m sure you know all this as you are an athlete, who needs to place great importance on diet .


I wrote a very detailed reply on another forum thread with links to B12 books, B12 websites, UK B12 documents and other b12 info.

There might be some useful info for you. I'm in UK so some of the info may be UK specific.

Have you considered joining PAS (Pernicious Anaemia Society)?

PAS (Pernicious Anaemia Society)

Based in Wales, UK. Has members in other countries.


PAS tel no +44 (0)1656 769717 answerphone

PAS support groups in UK


Do you mind me asking which country you are in?

The way B12 deficiency and PA is treated varies from country to country. In US, B12 shots are often cyanocobalamin and in UK, hydroxycobalamin is used most often. There is also methylcobalamin and adenosycobalamin. The frequency of B12 injections can vary according to which country you are in.

B12 Deficiency Info website

B12 Awareness (US website) holds support meetings near Durham, UK

Stichting B12 Tekort (Dutch website with English articles)

I am not medically trained.

Doctors often don’t know about this. Oral supplementation is less effective than injection because the absorption mechanism is in the gut and if you have IF antibodies that mechanism is broken (which is why you aren’t simply getting it from your food) Ultimately most of us self inject to avoid the obstructions put in place by uninformed doctors etc. Without B12 you run risk of doing nerve damage long term because body requires B12 for neurological systems, mitochondria, red blood cell construction, etc. It’s Very Important nutrient.

Sorry for the info dump - you will have to go thru a learning curve and it’s challenging. But better than fatigue and further deterioration.

Good luck 🙏🏼

It is not more than just a vitamin. It’s cost maneuver to try to move people to pills.

As stated above, the sudden onset is probably a correlation. In regards to the IFA seemingly being triggered I experienced something similar. Been fatigued for years, but I attributed that to motherhood. Then after the birth of my second child my symptoms came out of nowhere and I could hardly function. It felt like labor “pushed me over the edge”, though I’m sure it’s not the cause. I’ve noticed since in times of high stress my B12 shots are less/ineffective at managing symptoms, so mono probably depleted your supply quickly (I’m obviously not a scientist, just speaking from experience).

Wishing you all the luck in your treatments getting you healthy. I’m conditioning myself for physical activity again and it’s extremely frustrating at how slow I need to take it. I’ve never been highly active and I’m annoyed, so I can’t imagine how difficult it is for the athletes on here.

Sleepybunny in reply to tradkita

Hi Tradkita,

"Then after the birth of my second child my symptoms came out of nowhere"

Just wondered if you had "gas and air mix" as pain relief during labour?

Gas and air mix contains nitrous oxide which inactivates B12 in the body.

Link below is a UK link about effects of nitrous oxide.

If link does not work then you could search online for " B12 deficiency nitrous oxide"

B12 books below mention effects of nitrous oxide.

"What You Need to Know About Pernicious Anaemia and B12 Deficiency" by Martyn Hooper

"Could it Be B12?: An Epidemic of Misdiagnoses" by Sally Pacholok and JJ. Stuart (USA authors)

Very comprehensive with lots of case studies.

More info on B12 websites in my first post on this thread.

tradkita in reply to Sleepybunny

No gas and air for me. The US doesn’t have that for labor yet, at least not in my area. I did read about gas and air from Could it be B12, as per your suggestion on someone else’s post when I first got here. It was a very helpful. Thank you for your suggestions.

Get good gastro and they must look with endoscopy (not blood test) for hpylori.

I also have EBV. It and chicken pox late etc may have been triggers.

I am 63. Had to coral pathologists and not diagnosed til 56. Probably 60 or 61 before smartest gastro found my hpylori,

You’re so young. Your body did good. Keep on regular shots.

You may also like...