AG B12 TESTING XDon’t rely on a single serum B12 level—use functional markers like MMA (and homocysteine when needed) for a truer picture of B12 deficiency.

 A

Here’s a bullet-gist summary of the video NutritionFacts.org — “The Best Way to Test for Vitamin B12 Deficiency” by Michael Greger M.D.:

• Many diagnoses of vitamin B12 deficiency are made (or dismissed) based solely on a single serum B12 blood test—which is problematic. (NutritionFacts.org)

• Key issues with the standard serum B12 test:

  • Large variability between labs (same blood sample can show very different results). (NutritionFacts.org)

  • Significant day-to-day variation in an individual’s B12 levels (e.g., variation of >100 points over 10 weeks). (NutritionFacts.org)

  • A person may have normal or even high serum B12, yet still have functional deficiency (symptoms or neurologic damage) because serum B12 alone isn’t always reliable. (NutritionFacts.org)

• Better assessment uses functional biomarkers of B12 status:

  • Methylmalonic acid (MMA)

  • Homocysteine
    These rise when B12 is insufficient even if serum B12 is “normal.” (NutritionFacts.org)

• However: functional tests also have limitations (e.g., kidney function can raise MMA, folate deficiency can raise homocysteine). (NutritionFacts.org)

• For patients with classic symptoms of B12 deficiency (e.g., neuropathy, numbness, “pins & needles”), Dr Greger suggests: if tests are inconclusive → consider a therapeutic trial of B12 supplementation, because waiting for perfect tests may miss the deficiency. (NutritionFacts.org)

• Bottom line: there is no perfect biomarker or testing algorithm for B12 deficiency; clinical judgment matters. (NutritionFacts.org)

• From a public-health perspective: ensuring adequate intake of B12 (via diet, fortification or supplementation) is easier than relying solely on testing. (NutritionFacts.org)

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If you like, I can pull out “top 5 practical take-aways” from the video for patients or clinicians.