Vitamin B12 (Cobalamin)
What This Test Measures
Essential vitamin for nerve function and red blood cell formation; deficiency causes macrocytic anemia and neuropathy.
Preparation
Serum B12 is unreliable if you are supplementing. The B12 Society recommends being free of all B12 supplements AND fortified foods/drinks for at least 4 months to get a true baseline serum reading — B12 is stored in the liver, not just blood, so shorter washout periods only clear what is in circulation. However, most clinical guidelines do not specify a washout period. For people actively supplementing, MMA (methylmalonic acid) and homocysteine are far more reliable markers of functional B12 status and are not affected by supplementation timing. If on B12 injections, test just before your next injection to capture your trough level.
Reflects common practices in thyroid, BHRT, and functional medicine communities. This may differ from standard clinical guidelines. Not medical advice — always discuss with your provider.
General guidelines only. Requirements vary by lab and individual. Confirm with your provider before adjusting any medications.
Turnaround Time
Varies by lab
Clinical Notes
Serum B12 may not reflect tissue status; methylmalonic acid is functional B12 test
ICD-10 Codes
Common diagnosis codes associated with this test. Codes are assigned by your provider.
Self-Pay Pricing
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Uses Quest Diagnostics network; generally lowest DTC prices; not available in NY, NJ, RI
Uses Quest and Labcorp; strong panel bundling; results in 1-3 days
Uses Quest and Labcorp networks; offers both individual tests and discounted panels
Uses Quest Diagnostics network; good panel pricing; established DTC provider
Uses both Quest and Labcorp networks; competitive pricing; broad test selection
Uses Labcorp network; known for supplement company; competitive lab test pricing
Uses Quest and Labcorp; no hidden draw or facility fees; moderate pricing
Labcorp consumer-direct platform; 2,000+ locations; results in 1-3 days
Quest Diagnostics consumer-direct platform; results in 1-2 days; 2,100+ locations nationwide
Primarily uses Labcorp network; popular for hormone panels; higher individual test prices
Lab Codes
Proprietary codes used by each lab for this test.
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For informational purposes only
This page is for educational and research purposes only and does not constitute medical advice, diagnosis, or treatment recommendations. ICD-10 and CPT codes are assigned by your healthcare provider. Always consult a qualified healthcare provider before ordering any lab test or making decisions about your health.