Elevated methylmalonic acid is a lab finding associated with which deficiency?

Elevated methylmalonic acid is a lab finding associated with which deficiency?

• A. B12 deficiency
• B. B9 deficiency
• C. Both B9 and B12
• D. None of the above

Answer: (A)

Elevated methylmalonic acid points to a problem with the B12-dependent step converting methylmalonyl-CoA to succinyl-CoA. This reaction requires vitamin B12 as a cofactor, so when B12 is deficient, methylmalonyl-CoA accumulates and is shunted to methylmalonic acid, raising its levels. Folate (B9) deficiency, on the other hand, disrupts homocysteine remethylation to methionine and tends to raise homocysteine but not methylmalonic acid. Therefore, a high MMA level is most specifically associated with B12 deficiency, helping distinguish it from B9 deficiency.

Elevated methylmalonic acid points to a problem with the B12-dependent step converting methylmalonyl-CoA to succinyl-CoA. This reaction requires vitamin B12 as a cofactor, so when B12 is deficient, methylmalonyl-CoA accumulates and is shunted to methylmalonic acid, raising its levels. Folate (B9) deficiency, on the other hand, disrupts homocysteine remethylation to methionine and tends to raise homocysteine but not methylmalonic acid. Therefore, a high MMA level is most specifically associated with B12 deficiency, helping distinguish it from B9 deficiency.