What does high B12 in blood mean when really high?

Needs evaluation. B12 is not toxic so high B12 due to taking it is not bad. If someone has high B12 without taking it then it can be a sign of serious problems including liver & kidney disease, myelproliferative disorders including leukemia & polycythemia vera & hypereosinophilic syndrome. High B12 does not cause these but caused by them. Further tests are needed to find the underlying cause: http://bit.ly/1hVpCY7.