Evaluating vitamin B12 deficiency, especially in those with borderline serum vitamin B12 results.
Vitamin B12 (cobalamin) is a cofactor in the conversion of methylmalonyl-CoA to succinyl-CoA. In vitamin B12 deficiency, this reaction is unable to proceed normally and results in accumulation of methylmalonic acid (MMA). Vitamin B12 is also required to convert homocysteine to methionine, therefore patients with vitamin B12 deficiency may also have elevated plasma homocysteine.
Vitamin B12 deficiency can present with glossitis, fatigue, peripheral neuropathy and can result in macrocytic anaemia. There are many causes of vitamin B12 deficiency including vegan diets, bariatric surgery, small bowel disease, nitrous oxide use, and pernicious anaemia. Newborns of vitamin B12 deficient mothers are at risk of vitamin B12 deficiency, especially if exclusively breast-fed.
Nitrous oxide inactivates vitamin B12 so that it is not able to function as a cofactor, resulting in elevated MMA and homocysteine. Vitamin B12 level may be low or normal.
Elevated levels of MMA can also result from rare inherited defects in the metabolism of MMA or vitamin B12.
Specialist Biochemistry
MMA
Gross haemolysis OK, gross lipemia OK, gross icterus OK
Refrigerated (preferred) 48 days, frozen 48 days
MMA
14 days
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