Is a vitamin B12 (B12) level of 190 picograms per milliliter (pg/mL) indicative of a deficiency?

Vitamin B12 Level of 190 pg/mL: Indeterminate Result Requiring Further Evaluation

A vitamin B12 level of 190 pg/mL falls within the indeterminate range (180-350 pg/mL or 133-258 pmol/L) and should be considered a possible vitamin B12 deficiency requiring further testing with methylmalonic acid (MMA) to confirm diagnosis. 1

Interpreting B12 Levels

According to the 2024 NICE guidelines, B12 test results should be interpreted as follows:

Total B12 concentrations	Likelihood of deficiency
Less than 180 ng/L (133 pmol/L)	Confirmed vitamin B12 deficiency
180-350 ng/L (133-258 pmol/L)	Indeterminate - possible vitamin B12 deficiency
More than 350 ng/L (258 pmol/L)	Vitamin B12 deficiency unlikely

Diagnostic Algorithm for Indeterminate B12 Results

1. For B12 level of 190 pg/mL:

   • This falls in the indeterminate range
   • Proceed with measuring serum methylmalonic acid (MMA) 1
   • MMA is a more reliable functional marker of B12 status

2. If MMA is elevated:

   • Confirms metabolic B12 deficiency
   • Treat as B12 deficiency even with "normal-low" serum B12 levels

3. If patient has symptoms of B12 deficiency:

   • Consider treatment even with indeterminate levels
   • "If there is doubt about vitamin B12 deficiency, it is better to treat" 1

Clinical Relevance of Indeterminate B12 Levels

Traditional cutoff values for B12 deficiency may miss many cases of functional deficiency:

• Metabolic B12 deficiency (B12 <258 pmol/L with elevated homocysteine or MMA) is frequently missed 1
• In the Framingham Study, 12% of elderly were identified as B12 deficient by serum levels alone, but an additional 50% had metabolic deficiency when MMA was measured 1
• Studies using functional markers show deficiency prevalence of 10-40% in elderly populations versus only 5.9% when using serum B12 alone 1

Common Symptoms to Evaluate

If B12 level is 190 pg/mL, assess for:

• Cognitive difficulties ("brain fog")
• Neurological symptoms:
  • Balance issues
  • Impaired gait
  • Pins and needles or numbness
  • Sensory ataxia
• Eyesight problems (blurred vision, optic atrophy)
• Glossitis
• Unexplained fatigue
• Macrocytosis or anemia 1

Risk Factors to Consider

Evaluate for risk factors that increase likelihood of true deficiency:

• Diet low in vitamin B12 (vegan/vegetarian)
• Medications (metformin, PPIs, H2 blockers, colchicine)
• Atrophic gastritis
• Autoimmune conditions (thyroid disease, type 1 diabetes)
• Age >75 years
• Malabsorptive conditions 1, 2

Common Pitfalls in B12 Assessment

1. Relying solely on serum B12 levels:

   • Serum B12 in the "normal range" doesn't rule out deficiency
   • Functional markers (MMA, homocysteine) are more sensitive 1

2. Missing neurological damage:

   • Neurological symptoms can occur without anemia
   • Neurological damage may become irreversible if treatment is delayed 3

3. Inadequate testing in high-risk groups:

   • Elderly patients (>75 years)
   • Those on long-term metformin or acid-suppressing medications
   • Post-bariatric surgery patients 1, 4

Treatment Considerations

If deficiency is confirmed with MMA testing:

• Oral high-dose vitamin B12 (1-2 mg daily) is as effective as intramuscular administration for most patients 2, 5
• Intramuscular therapy should be considered for severe deficiency or severe neurological symptoms
• Treatment should be prompt to prevent irreversible neurological damage 3

In summary, a B12 level of 190 pg/mL requires further evaluation with MMA testing to confirm or rule out true vitamin B12 deficiency, as this value falls within the indeterminate range where metabolic deficiency may be present despite "normal-low" serum levels.