Causes of high B12 levels in the blood include serious medical conditions like hepatitis and cirrhosis, chronic myelocytic leukemia and a bone marrow disorder, according to MedlinePlus. Test results may be incorrect in some cases due to supplement intake, according to Mayo Medical Laboratories.
People who take B12 supplements or Vitamins C or A can have misleading test results, according to Mayo Medical Laboratories. Ingestion of estrogen, conditions like uremia and certain injuries can also produce a false B12 serum level during testing. Some patients who are exposed to animal antigens have a false result during testing because anti-animal antibodies are present.