B12 Testing: When Should You Get Your Blood Checked

When You Should Consider Testing

• You've been vegetarian (especially vegan) for over 6 months and have never been tested
• You notice possible symptoms like fatigue, tingling or numbness, or memory decline
• You're trying to conceive, pregnant, or breastfeeding
• You're over 60, since gut absorption naturally declines with age
• You've been on long-term acid-reducing medication (proton pump inhibitors) or have had gastrointestinal surgery

Common Markers to Check

• Serum B12: The standard screening marker, though its sensitivity is limited in borderline ranges
• Homocysteine: Typically elevated with B12 or folate deficiency, making it a useful supporting marker
• Methylmalonic acid (MMA): Rises specifically with B12 deficiency, making it a more sensitive indicator of whether cellular B12 is truly adequate

How Often to Test

If you're stable on a supplement routine with no symptoms, testing once a year is enough; if you're adjusting your supplement plan or experiencing symptoms, you can shorten the testing interval as your doctor advises. It's best to interpret results alongside homocysteine and other markers, since serum B12 alone can sometimes underestimate the true extent of a deficiency. This test is generally inexpensive, and can often be added on to a routine physical exam panel without a separate appointment.