Yes, 1900 is very high. Without using ANY form of vitamin containing B12, the suspects are, liver damage, kidney disease of some kind, or a myeloproliferative (bone marrow) disease (mostly cancers).

An MMA test would show if B12 is working in the body, and not just floating around.

I think your doctor should do something, if only a few more tests, to see if it warrants looking for a hidden disease.

Most B complexes have B12 in them, and some breakfast cereals, and energy bars. If you consume them before the test, you could test high. But as a comparison, I tested at 1999 (from 849 normally) when I tried the new at the time Puritan's methylB12 in the recent past. I took 5mg orally in the morning on an empty stomach and 3 months later tested at that high level. My doctor was convinced that oral cannot work and was surprised that it did seem to work very effectively for me!

One should stop all vitamin supplements 3 to 5 days before any further testing to obtain a more accurate result.