I've been under investigation for nearly a year with symptoms that matched B12 deficiency (and all of the other things with similar symptoms!). I was originally referred by my GP to an endocrinologist with suspected thyroid dysfunction, but subsequent tests ruled this out. I also had tests for adrenal function, PA, coeliac disease, iron and B12 and D deficiency, plus a CT head scan. My B12 was at 121 and D was also low, but everything else came back normal. The endo prescribed a strong vit D but said my B12 wasn't low enough to worry about and that I could take a supplement if I wanted to but that it wasn't really necessary.
I didn't know anything about B12 deficiency at the time but when I looked into it and realised the symptoms matched mine, I started taking a supplement in tablet form. Nothing changed after about a month, I was still having worse and worse symptoms, so in desperation I decided to try an oral spray (48,000% RDA) to see if that helped. It was amazing! Within a week I began to feel better and after a couple more weeks my symptoms had pretty much gone. I also discovered from online research that Metformin (which I've been on for 2 years for insulin resistance) can cause you to become deficient in B12.
It seemed pretty clear that this was what had been causing my symptoms, but when I discussed this with my endo at my next appointment, despite him not having found any other explanation for my symptoms, he said it was a coincidence and that since I didn't have PA it couldn't be anything to do with my B12! He said he didn't know anything about Metformin affecting B12 (even though it's listed as a side effect on the packaging!) and that if I was low in B12 then it was undoubtedly because I wasn't eating properly (in fact I eat a very balanced diet including plenty of food with B12) but that this wouldn't cause me any problems unless I had PA. He wanted to discharge me and refer me on to gastroenterology, since I'd had gastro symptoms as well as everything else.
Well at this point I was pretty fed up of endless inconclusive tests and patronising doctors, and since I was feeling so much better, I just left it at that. I figured that if I wasn't absorbing B12 for a reason other than PA or Metformin then the gastro might find it. I waited months for a gastro appointment but I've had various tests and the only thing that has come back abnormal is that I'm mildly lactose intolerant, which I knew already. I asked the gastro if anything could cause me to not absorb B12 properly and she said not specifically.
My questions now are about what to do next. I did an experiment recently where I stopped taking the oral spray and within a few days I started to feel a bit unwell and after a week all of my symptoms had come back as bad as they were before. I could just keep taking the spray, since it's working, but I'm concerned about the long term if something has been missed which is causing me not to absorb or store B12 properly. Has anyone else had problems with B12 despite not having PA? Anyone on Metformin noticed the link?