When should MMA and homocysteine be checked?

In the borderline range (200-300 pg/mL), elevated methylmalonic acid (MMA) and homocysteine indicate functional B12 deficiency even with normal serum levels. MMA is more specific (elevated in 98% of deficient patients vs. homocysteine at 95%).

What are the clinical features of B12 deficiency?

Megaloblastic anemia (macrocytosis, hypersegmented neutrophils), subacute combined degeneration of the spinal cord (posterior column and corticospinal tract demyelination causing paresthesias, ataxia, spasticity), glossitis, and cognitive impairment.

Can oral B12 treat deficiency in pernicious anemia?

Yes. High-dose oral B12 (1000-2000 mcg/day) can treat even pernicious anemia via passive absorption (1% of any dose is absorbed by passive diffusion independent of intrinsic factor). However, IM cyanocobalamin is preferred for neurological complications.

Vitamin B12 Deficiency Interpretation

Interpret serum vitamin B12 levels. Deficient: below 200 pg/mL (requires supplementation). Borderline/grey zone: 200-300 pg/mL (check methylmalonic acid and homocysteine for functional deficiency). Normal: above 300 pg/mL. Causes: pernicious anemia, gastric atrophy, strict veganism, metformin use, gastric bypass, H. pylori infection.

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Frequently Asked Questions

When should MMA and homocysteine be checked?

What are the clinical features of B12 deficiency?

Can oral B12 treat deficiency in pernicious anemia?