What Is a Methylmalonic Acid (MMA) Test?
Methylmalonic acid (MMA) accumulates when vitamin B12 is deficient. It rises earlier than serum B12 drops.
Why MMA Is Useful
- More sensitive than serum B12
- Detects functional deficiency
- Useful when B12 is borderline (200–400 pg/mL)
- Not affected by recent B12 supplementation as quickly
Normal Range
- Below 0.4 µmol/L
- Above 0.4 = B12 deficiency likely
When to Order
- B12 is 200–400 pg/mL with symptoms
- Neuropathy with normal B12
- Before starting lifelong B12 supplementation
Source: NLM MedlinePlus, AACC.
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