Translations:Vitamin B12/27/en

Diagnosis

According to one review: "At present, no 'gold standard' test exists for the diagnosis of vitamin B₁₂ deficiency and as a consequence the diagnosis requires consideration of both the clinical state of the patient and the results of investigations." The vitamin deficiency is typically suspected when a routine complete blood count shows anemia with an elevated mean corpuscular volume (MCV). In addition, on the peripheral blood smear, macrocytes and hypersegmented polymorphonuclear leukocytes may be seen. Diagnosis is supported based on vitamin B₁₂ blood levels below 150–180 pmol/L (200–250 pg/mL) in adults. However, serum values can be maintained while tissue B₁₂ stores are becoming depleted. Therefore, serum B₁₂ values above the cut-off point of deficiency do not necessarily confirm adequate B₁₂ status. For this reason, elevated serum homocysteine over 15 micromol/L and methylmalonic acid (MMA) over 0.271 micromol/L are considered better indicators of B₁₂ deficiency, rather than relying only on the concentration of B₁₂ in blood. However, elevated MMA is not conclusive, as it is seen in people with B₁₂ deficiency, but also in elderly people who have renal insufficiency, and elevated homocysteine is not conclusive, as it is also seen in people with folate deficiency. In addition, elevated methylmalonic acid levels may also be related to metabolic disorders such as methylmalonic acidemia. If nervous system damage is present and blood testing is inconclusive, a lumbar puncture may be carried out to measure cerebrospinal fluid B₁₂ levels.