Patients with subacute combined spinal cord degeneration (SCD) from chronic nitrous oxide abuse will often have elevated levels of methylmalonic acid and homocysteine. Which is more specific for B12 deficiency?
MMA elevation is more specific for B12 deficiency because homocysteine may be elevated with folate deficiency as well.
Courtney Temple & B. Zane Horowitz (2022) Nitrous oxide abuse induced subacute combined degeneration despite patient initiated B12 supplementation, Clinical Toxicology, 60:7, 872-
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