[mrsD]

There is no upper limit on B12 medically. (not toxicity studies)

The out of range upper figure is only useful for those patients NOT taking any supplements before the testing. The ranges were
developed on people not using any supplements, currently or in the recent past.

So the upper readings out of range can imply some medical condition (kidney failure, some cancers, liver disease, etc) being present, that needs further evaluation.

Excess B12 that is not used, or stored by the liver is excreted by the kidneys.

However, some doctors react to high B12 readings with horror...and tell people to stop supplements. This indicates a poorly trained doctor who doesn't understand the test's meaning. I myself would find another doctor who can evaluate things more realistically.