Vitamin B12 optimal range and reference range

Compiled by Alina Radu, founder of Sera, from the published sources below · Last reviewed November 9, 2026

Sera's bands for Vitamin B12:

Optimal 500 – 900 pg/mL (369 – 664 pmol/L); sufficient 200 – 1,500 pg/mL (148 – 1,100 pmol/L); out of range below 200 or above 1,500 pg/mL.

Evidence grade: Functional / longevity target. A narrower target in common use in functional, integrative, preventive and longevity practice. It is not a universally validated diagnostic range.

At Sera's last range review a change to this band was proposed and held, because the evidence for it was thin, so the band is unchanged. The note below says where it matches published intervals and where it does not.

All units

Unit	Optimal	Sufficient	Out of range
pg/mL	500 – 900	200 – 1,500	below 200 or above 1,500
pmol/L	369 – 664	148 – 1,100	below 148 or above 1,100
ng/L	500 – 900	200 – 1,500	below 200 or above 1,500

What the evidence says

Total B12 includes the fraction bound to haptocorrin, which is not available to cells. A result in the lower half with symptoms is worth following with methylmalonic acid or active B12. The acceptable lower edge of 200 pg/mL (148 pmol/L) is where most laboratories call a result low; NICE treats below 180 ng/L as confirmed deficiency and 180 to 350 as indeterminate. The optimal lower edge of 500 is above every published figure and is a functional target. The acceptable upper edge of 1500 has no source: the highest laboratory upper limit confirmed is 1245.

Sources

Vitamin B12 - Health Professional Fact Sheet — NIH Office of Dietary Supplements, 2025 · Government / public-health guidanceMost laboratories define subnormal serum B12 as below 200 or 250 pg/mL (148 or 185 pmol/L); MMA should be checked when B12 is 150 to 399 pg/mL. Matches Sera's sufficient lower edge of 200 pg/mL exactly. Updated July 2, 2025.
Vitamin B12 deficiency in over 16s: diagnosis and management (NG239), Recommendations, Table 1 — National Institute for Health and Care Excellence (NICE), 2024 · Clinical guidelineTotal B12 below 180 ng/L (133 pmol/L) is confirmed deficiency, 180 to 350 ng/L (133 to 258 pmol/L) is indeterminate, above 350 ng/L makes deficiency unlikely. Supports Sera's note that a lower-half result with symptoms needs follow-up; does not reach Sera's optimal lower edge of 500.
B12 - Vitamin B12 Assay, Serum: Clinical & Interpretive — Mayo Clinic Laboratories, 2026 · Laboratory / reference-interval sourceReference values 180 to 914 ng/L; below 150 is evidence of deficiency and 150 to 400 is borderline, to be followed with methylmalonic acid or homocysteine. The upper limit of 914 is close to Sera's optimal upper edge of 900.
Vitamin B12 — Labcorp, 2026 · Laboratory / reference-interval sourceReference range 232 to 1245 pg/mL. The highest verified laboratory upper limit; Sera's sufficient upper edge of 1500 is above it.

What Vitamin B12 (Total) measures

The standard vitamin B12 test, which counts both the usable and the unusable forms of a vitamin your body needs for healthy nerves and for making energy.

Low B12 can cause fatigue, nerve problems, and trouble with memory and thinking. Most of what this test counts is bound to a carrier your cells cannot use, so a normal result does not always rule a shortfall out.

Related vitamins & minerals markers

See Vitamin B12 in the full list of biomarker ranges

This page is a reference for practitioners, not medical advice. Sera's bands are practitioner targets for structured review, not diagnostic thresholds, and Sera does not diagnose or recommend treatment. Read a result alongside the interval printed by the issuing laboratory and the client's history and symptoms. Range set: Sera Production, version 1.0, last reviewed November 9, 2026.