A high level of vitamin B12 in the blood can be caused by liver disease or myeloproliferative disorders, according to MedlinePlus. Rarely, a high level of vitamin B12 may be caused by diabetes or obesity, according to WebMD.
Liver diseases that can cause a high vitamin B12 level are cirrhosis and hepatitis, according to MedlinePlus. Myelproliferative disorders that may be due to a high vitamin B12 level are chronic myelocytic leukemia and polycythemia vera.
Vitamin B12 levels are measured through a vitamin B12 level blood test, also referred to as a cobalamin test, according to MedlinePlus. Increased vitamin B12 levels are uncommon, because excess vitamin B12 is usually eliminated with urine.
Normal vitamin B12 levels vary throughout different labs. WebMD lists a guide for normal vitamin B12 level as between 110 and 1500 picograms per milliliter. An individual’s doctor evaluates the test results with the individual’s health and other factors in mind.
Medications such as colchicine, phenytoin, para-aminosalicyclic acid and neomycin may affect vitamin B12 blood test results, according to MedlinePlus. An individual should talk with the doctor about medication use before taking the test. An individual should also not eat or drink for approximately six to eight hours before taking the test.