For me it was detected through a stomach biopsy. I have antibodies to cells that create intrinsic factor and also antibodies to intrinsic factor. And all my cels are gone that produce it. Without intrinsic factor you cannot move b12 into your blood stream. Without b12 you can die in 5 years unless you inject. If you inject enough you have a normal life. You can not overdose. Every cell in your body needs 12. without it your nerves deteriorate first. Doctors don’t usually know much about it but it probably affects way more people especially old than are ever tested. The normal b12 blood tests are only 50% accurate- so basically useless. There is a great facebook group with 60000 members. I learned a lot about it in Rotterdam at a b12 convention. One doctor there said if the test are useless why don’t we inject everyone who has symptoms with b12 every other day and see if they get better in 6 weeks since it can’t hurt. But the protocols are old and there is not enough research so they don’t have the power to try it. But you can. Hope you feel better soon.