Vitamin B12: What Your Results Mean
Bottom line: Vitamin B12 is essential for nerve function and red blood cell production. Normal is 300-900 pg/mL. Low B12 causes fatigue, numbness, and anemia.
What Is Vitamin B12?
Vitamin B12 (cobalamin) is a water-soluble vitamin that plays a critical role in nerve function, DNA synthesis, and red blood cell formation. Unlike most vitamins, B12 is found almost exclusively in animal-derived foods, making deficiency common among vegans, vegetarians, and older adults.
Your body stores several years' worth of B12 in the liver, so deficiency develops gradually. By the time symptoms appear, levels may have been low for months or years. This makes blood testing especially important for at-risk groups.
B12 deficiency affects an estimated 6% of adults under 60 and nearly 20% of those over 60 in the United States. Many cases go undiagnosed because symptoms overlap with other conditions.
Vitamin B12 Reference Ranges
| Classification | Range (pg/mL) |
|---|---|
| Severely Deficient | Below 100 |
| Deficient | 100 - 199 |
| Borderline Low | 200 - 299 |
| Normal | 300 - 900 |
| High | Above 900 |
What Affects Your Vitamin B12 Levels?
- Diet (vegans and vegetarians are at higher risk of deficiency)
- Age (absorption decreases after 50)
- Pernicious anemia (autoimmune condition that prevents B12 absorption)
- Gastrointestinal conditions (celiac disease, Crohn's, gastric bypass surgery)
- Medications (metformin, proton pump inhibitors, H2 blockers)
- Alcohol use (impairs absorption and depletes stores)
When to Get Tested
Consider B12 testing if you experience unexplained fatigue, numbness or tingling, difficulty concentrating, or if you follow a vegan or vegetarian diet. Adults over 50 should have B12 levels checked regularly. If you take metformin or proton pump inhibitors long-term, periodic monitoring is recommended.
Look Up Your Vitamin B12 Result
Select your value below to see a detailed breakdown of what it means:
Deficient
Borderline Low
Normal
High
Read the Full Blood Test Guide
Frequently Asked Questions
The normal range for Vitamin B12 is 300-900 pg/mL. Levels below 200 pg/mL are considered deficient, while 200-299 pg/mL is borderline low. Levels above 900 pg/mL are considered high and may warrant investigation.
Common causes include poor dietary intake (especially in vegans and vegetarians), pernicious anemia, malabsorption conditions like celiac disease or Crohn's disease, certain medications (metformin, proton pump inhibitors), and aging, which reduces absorption efficiency.
Symptoms include fatigue, weakness, numbness or tingling in hands and feet, difficulty walking, cognitive difficulties, mood changes, and pale or yellowish skin. Severe deficiency can cause irreversible nerve damage if left untreated.
Commonly Seen Together
Blood test results rarely exist in isolation. When one marker is out of range, these related values are often checked alongside it: