Differential Diagnosis for Very High Vitamin B12 Level

• Single Most Likely Diagnosis
  • Recent vitamin B12 injection or supplementation: This is the most common cause of elevated vitamin B12 levels, as the body stores excess vitamin B12 in the liver, and high doses can lead to elevated serum levels.
• Other Likely Diagnoses
  • Myeloproliferative neoplasms (e.g., polycythemia vera, chronic myeloid leukemia): These conditions can increase vitamin B12 levels due to increased production of transcobalamin I, a protein that binds to vitamin B12.
  • Liver disease (e.g., liver cirrhosis, liver cancer): The liver stores and metabolizes vitamin B12, and liver disease can lead to the release of stored vitamin B12 into the bloodstream, causing elevated levels.
  • Kidney disease: Impaired kidney function can lead to decreased excretion of vitamin B12, resulting in elevated serum levels.
• Do Not Miss Diagnoses
  • Leukemia (e.g., acute myeloid leukemia): Although less common, leukemia can cause elevated vitamin B12 levels due to increased cell turnover and release of vitamin B12 from lysed cells.
  • Solid tumors (e.g., breast, lung, or colon cancer): Some solid tumors can produce transcobalamin I, leading to elevated vitamin B12 levels.
• Rare Diagnoses
  • Transcobalamin II deficiency: A rare genetic disorder that affects the transport of vitamin B12, leading to elevated serum levels.
  • Pernicious anemia (with recent treatment): Although pernicious anemia typically causes low vitamin B12 levels, recent treatment with vitamin B12 injections can lead to elevated levels.
  • Familial hypercobalaminemia: A rare genetic disorder characterized by elevated vitamin B12 levels due to increased production of transcobalamin I.