Treatment Recommendation for B12 Deficiency
For this 60-year-old female with confirmed B12 deficiency (112 pmol/L), initiate oral cyanocobalamin 2,000 mcg daily for 3 months, then reassess. 1
Initial Treatment Approach
Oral therapy is the preferred first-line treatment for B12 deficiency in patients without neurological symptoms or severe malabsorption. 1 The evidence supports that oral supplementation at high doses (1,000-2,000 mcg daily) achieves therapeutic equivalence to intramuscular therapy through passive absorption, even in malabsorption states. 2, 3
Specific Dosing Protocol
- Start with oral cyanocobalamin 2,000 mcg daily on days 1,3,7,10,14,21, then transition to monthly dosing 1
- This regimen is effective because high-dose oral B12 bypasses the need for intrinsic factor through passive diffusion, with approximately 1-2% absorption even without active transport 3
When to Consider Intramuscular Therapy Instead
Switch to intramuscular administration if any of the following are present:
- Neurological symptoms (paresthesias, gait disturbances, cognitive changes, subacute combined degeneration) - these require immediate IM therapy 4, 5
- Severe deficiency with symptoms requiring rapid correction 3
- Known malabsorption conditions: pernicious anemia, post-gastrectomy, ileal resection, inflammatory bowel disease 6
For IM therapy when indicated: cyanocobalamin 1,000 mcg IM - give on days 1-10 (or alternate days for 2 weeks), then monthly for life 1, 6
Critical Assessment Before Treatment
You must evaluate for neurological involvement before starting therapy, as this changes the treatment urgency and route:
- Ask about: numbness/tingling in extremities, balance problems, memory issues, confusion 5, 7
- Examine: proprioception, vibration sense, gait, mental status 7
- If neurological symptoms present: use IM hydroxocobalamin 1 mg on alternate days until no further improvement, then every 2 months for life 4
The Normal CBC Paradox
The normal CBC with slightly elevated RBC count (5.16) does not exclude B12 deficiency. 7 This presentation is important to recognize:
- B12 deficiency classically causes macrocytic anemia, but early or mild deficiency may not show hematologic changes 7
- The elevated RBC count could represent a compensatory response or be unrelated 7
- Neurological damage can occur before hematologic abnormalities develop - this is a critical pitfall 5, 7
Monitoring and Follow-up
Reassess after 3 months of treatment: 1
- Recheck serum B12 level (target >300 pmol/L) 3
- If available, measure methylmalonic acid and homocysteine to confirm metabolic correction 2, 3
- Evaluate symptom resolution 5
After initial correction, continue maintenance therapy indefinitely if the underlying cause cannot be reversed (dietary insufficiency may be correctable, but malabsorption typically requires lifelong treatment). 5
Critical Pitfall to Avoid
Never give folic acid before or without treating B12 deficiency - this can mask the hematologic manifestations while allowing neurological damage to progress (subacute combined degeneration of the spinal cord). 4 If folate deficiency coexists, treat B12 first or simultaneously. 6
Determining the Underlying Cause
Investigate why this patient is B12 deficient:
- Dietary history: strict vegetarian/vegan diet 3
- Medication review: metformin >4 months, PPIs or H2 blockers >12 months 3
- GI history: gastric surgery, inflammatory bowel disease, chronic diarrhea 6, 3
- Consider testing for pernicious anemia if no obvious cause: anti-intrinsic factor antibodies, anti-parietal cell antibodies 2, 7
The cause determines whether oral therapy will suffice long-term or if IM therapy is ultimately needed. 5