Unconfirmed PA, but B12d diagnosed here too, so is DD, PA is only one reason why you cant absorb B12 though, theres others. There's several reasons why B12 can suddenly drop too.
Lots of PA in my family, so thats most likely for us, NICE recognise that ID, PCA & Serum B12 tests are all unreliable, so a negative PA test doesn't mean you don't have PA, but a positive test does.
Heliobacter Pylori infection is another much more common reason for B12d, it causes Gastritis, so it can affect food digestion/nutrient absordtion, there are other reasons too.
The blood chemistry around B12d & other Vits & minerals is complicated & certain other deficiencies can mask B12d as they work together, so correcting that deficiency might mean your getting a more accurate B12 reading now.
The NHS Serum B12 testing isn't really much good, it measures all the B12 in your blood, not what your body can use, you just we the unused stuff out, but it will still show in your blood for a while. So it might be higher if you have had meals rich in B12 or were taking supplements or eating fortified foods before your blood was taken. It could have dropped if you were tested on a day where you had eaten less B12 etc.
Plus theres a long list of drugs that deplete B12, even Gas & Air used in childbirth/some dental work etc, Also pregnancy as your DC gets its B12 stores from you, if your B12 is ok, you suddenly end up low.
Lots of reasons, I'm not medical or anything, but B12d/PA is massively misunderstood by too many Doctors. You've been lucky, sounds like you have a good Doctor. Too many of us have to fight for testing & treatment, so we have to learn & educate our Drs as for the most part, they don't have a lot of training in deficiencies & often misunderstand the guidelines too.
But, treatment can make a world of difference, you do need to take other vitamins & minerals too, as B12 needs these cofactors to work. You need to be taking...
5mg of Folic Acid, (thats 12 of the 400mg ones) whilst you are on your loading dose,
Magnesium(not oxide)
Complete B vits(for a lower dose B6)
plenty of potassium rich foods
lower dose iron supplement such as Feroglobin
My DD was very ill, on a good day, she stuck in a wheelchair, in severe pain, raging anxiety, barely slept & much more. I knew we had PA in our family, but it had supposedly been ruled. finding out SIL had the hereditary type too, I've had to learn this stuff so I could fight for treatment for her sake. I will come back with links to my sources of info. DD who missed nearly 2 years of school is now back on her feet, back in school & is out dancing at a halloween party with her friends tonight
. She gets monthly injections