Originally Posted by mrsD

B12 can be elevated from some disease states.

Leukemia is one. Other blood diseases also. A severe imbalance of organisms in the bowel, from using too many antibiotics may do it. Also some forms of kidney failure, show up with high B12.

Many foods are fortified now, including cereals. So read your labels to see if some is sneaking in that way.
Also if you are tested while taking vitamins containing B12 you may be elevated.

2000 is typically the highest reading in US because that is how high the machines are calibrated today at the labs.

I took a high dose supplement for 3 months daily 5mg of methylcobalamin and got a high reading like yours.

One long shot is if your B12 cannot convert to active form, methylB12 in the body, it may build up too. Another test called the MMA test will show if B12 is working in your system. It should test LOW to be normal. When B12 (and folate) are not converted by the body, this shows a genetic error called MTHFR polymorphism. There is a DNA blood test then to show if you have this problem. Taking methylfolate and methylcobalamin bypasses this error. People with this genetic mutation also have high homocysteine levels, which over time damages blood vessels leading to heart attack and strokes.