Can this result diagnose a condition on its own?

No. Laboratory results are interpreted with symptoms, medical history, specimen conditions and related tests.

Which reference range should I use?

Start with the performing laboratory's own reference interval; clinical cutoffs, when relevant, are separate sourced thresholds used for a specific purpose.

When should I discuss the result with a healthcare professional?

Results that are clearly outside range, persistent, symptomatic or unexpected should be reviewed by a healthcare professional.

Information about a laboratory test

Low Vitamin B12: What Does It Mean?

Low B12 can occur with inadequate intake or malabsorption. MMA and homocysteine can add context when serum B12 is borderline.

Test summary

Test name: Vitamin B12
Abbreviations: B12, Cobalamin
Category: Vitamins / B-Complex
Panel: Nutritional / Anemia Evaluation
Specimen: Serum / plasma
Common units: pg/mL, pmol/L

What does the test measure?

The Vitamin B12 test measures neurologic function, DNA synthesis and red-blood-cell formation.

Why is the test ordered?

Ordered when inadequate intake or absorption is suspected, in risk groups, or to assess supplement use; it is interpreted with related laboratory tests.

Information about a low result

Low B12 can occur with inadequate intake or malabsorption. MMA and homocysteine can add context when serum B12 is borderline.

Information about a high result

High B12 can follow supplements or injections. Persistent unexpected elevation should not be interpreted simply as excessive intake and needs clinical context.

Reference and clinical context

Start with the performing laboratory's reference interval, unit, specimen type and method. Numeric information on this page is stored as sourced example intervals or clinical thresholds.

Reference context 1

< 200 pg/mL

Population: Adults / general clinical use
Age range: 18
Specimen: Serum / plasma

Commonly used low vitamin B12 threshold

This is a sourced clinical-context threshold and should not be used alone as a diagnosis or treatment decision. The laboratory report and clinical context take priority.

Reference context 2

>= 150 – <= 399 pg/mL

Population: Adults / confirmatory-testing context
Age range: 18
Specimen: Serum / plasma

B12 range where MMA can provide additional assessment

This is a sourced clinical-context threshold and should not be used alone as a diagnosis or treatment decision. The laboratory report and clinical context take priority.

Reference ranges may vary by laboratory, method used, age, sex, pregnancy status, and clinical context. The reference range on your own laboratory report takes precedence.

Interpretation notes

B12 cutoffs vary by method. Methylmalonic acid is a sensitive functional marker when serum B12 is borderline, but kidney function can affect MMA.

Related specialties

Internal Medicine
Hematology
Gastroenterology
Family Medicine

Frequently asked questions

Sources

Vitamin B12 – Health Professional Fact Sheet — NIH Office of Dietary Supplements
U.S. government nutrition reference · 2025 · Vitamin B12 status, serum B12, MMA and homocysteine interpretation · Verified: Aug 12, 2026
Folate – Health Professional Fact Sheet — NIH Office of Dietary Supplements
U.S. government nutrition reference · 2022 · Serum/RBC folate status and homocysteine context · Verified: Aug 12, 2026
Methylmalonic Acid (MMA) Test — U.S. National Library of Medicine (MedlinePlus)
Government medical reference · 2024 · MMA testing in vitamin B12 deficiency and meaning of high/low results · Verified: Aug 12, 2026
Homocysteine Test — U.S. National Library of Medicine (MedlinePlus)
Government medical reference · 2025 · Homocysteine relation to B vitamins, confounders and testing limitations · Verified: Aug 12, 2026