In an elderly male resident of an independent‑living facility with mild normocytic anemia (hemoglobin 12.3 g/dL, hematocrit 35.9 %, mean corpuscular volume 90 fL), low serum iron, low total iron‑binding capacity, normal ferritin, and markedly low vitamin B12 (92 pg/mL), what is the most likely cause of his anemia and how should it be managed?

Vitamin B12 Deficiency is the Primary Cause—Immediate Intramuscular Replacement is Required

This elderly male has severe vitamin B12 deficiency (92 pg/mL, normal >200 pg/mL) causing his mild normocytic anemia, and he requires immediate intramuscular cyanocobalamin 1000 mcg daily for one week, then weekly for one month, followed by monthly injections for life to prevent irreversible neurological damage. 1

Diagnostic Interpretation

The laboratory findings point definitively to vitamin B12 deficiency as the primary etiology:

• Markedly low B12 at 92 pg/mL is well below the normal range and diagnostic of deficiency 1
• Mild normocytic anemia (Hgb 12.3 g/dL, MCV 90.2 fL) is consistent with early B12 deficiency before macrocytosis develops 2
• Normal ferritin (62 ng/mL), folate (18 ng/mL), and iron studies exclude iron deficiency and folate deficiency as causes 2
• Normal renal function (GFR 85, creatinine 0.9) rules out anemia of chronic kidney disease 2
• Absence of inflammation markers and normal liver enzymes make anemia of chronic disease unlikely 2

The normocytic presentation is typical in elderly patients with B12 deficiency, as anemia in this population is often mild (10-12 g/dL) and may not yet show macrocytosis 3. The MCV of 90 fL sits at the upper end of normal, suggesting early evolution toward macrocytic changes 2.

Urgent Treatment Protocol

Immediate Intramuscular Therapy

Initiate cyanocobalamin 1000 mcg intramuscularly immediately using the following regimen 1:

• Loading phase: 1000 mcg IM daily for 7 days
• Consolidation phase: 1000 mcg IM weekly for 4 weeks
• Maintenance phase: 1000 mcg IM monthly for life

Critical Rationale for Parenteral Route

Oral supplementation is inadequate in elderly patients because 1:

• Absorption may be impaired due to intrinsic factor deficiency (pernicious anemia), atrophic gastritis, or malabsorption
• The independent living facility setting suggests potential dietary insufficiency and poor oral compliance
• Intramuscular administration bypasses absorption issues and ensures adequate repletion

Monitoring Requirements

Obtain baseline and follow-up laboratory studies 1:

• Serum potassium within 48 hours of initiating treatment—hypokalemia can occur as marrow activity increases during B12 repletion 1
• Reticulocyte count at days 5-7 to confirm marrow response (should increase to at least twice normal) 1
• Repeat hemoglobin and hematocrit at 2-4 weeks to document improvement 1
• Reassess B12 level at 3 months to confirm adequate repletion

Investigation of Underlying Cause

While treating the deficiency, investigate the etiology 2:

• Screen for pernicious anemia: Anti-intrinsic factor antibodies and anti-parietal cell antibodies
• Evaluate for malabsorption: Consider upper endoscopy with duodenal biopsies to exclude celiac disease (present in 2-3% of nutritional deficiency cases) 4
• Assess dietary intake: A strict vegetarian diet containing no animal products causes B12 deficiency 1
• Review medications: Metformin, proton pump inhibitors, and H2-blockers impair B12 absorption 1
• Consider gastric pathology: Patients with pernicious anemia have 3 times the incidence of gastric carcinoma 1

Critical Pitfalls to Avoid

Never Use Folic Acid Alone

Do not administer folic acid without concurrent B12 replacement—folic acid doses >0.1 mg daily may correct the anemia but allow progression of irreversible subacute combined degeneration of the spinal cord 1. This is a medical emergency that must be prevented.

Do Not Delay Treatment

Vitamin B12 deficiency progressing beyond 3 months produces permanent degenerative spinal cord lesions 1. Given the patient's age and living situation, neurological symptoms may already be present but attributed to "normal aging." Immediate treatment is mandatory.

Recognize That Oral Therapy is Insufficient

Although some guidelines mention oral B12 for maintenance, this elderly patient in an independent living facility requires parenteral therapy to ensure compliance and adequate absorption 1. Monthly injections for life are non-negotiable.

Monitor for Coexisting Deficiencies

The normal folate and iron studies are reassuring, but combined deficiencies can occur 2, 4. If the reticulocyte response is inadequate at days 5-7, reassess iron and folate levels 1.

Educate the Patient and Facility

The patient must understand that monthly B12 injections are required for life—failure to continue treatment will result in recurrence of anemia and development of incapacitating, irreversible neurological damage 1. Coordinate with the independent living facility to ensure injections are administered reliably.

Expected Clinical Response

With appropriate treatment 1:

• Reticulocyte count should rise by days 5-7 and remain at least twice normal until hematocrit normalizes
• Hemoglobin should increase by ≥1 g/dL within 2-4 weeks
• Neurological symptoms (if present) may improve but will not reverse if treatment is delayed beyond 3 months

If the expected hematologic response does not occur, reevaluate the diagnosis and consider complicating factors such as occult blood loss, renal disease, or myelodysplastic syndrome 2, 1.