What is the diagnosis in a 72-year-old woman with hemoglobin 10.2 g/dL, mean corpuscular volume (MCV) 102 fL, neutrophilia on blood smear, ferritin 220 ng/mL, vitamin B12 210 pg/mL, folate 12 ng/mL, and methylmalonic acid 580 nmol/L?

Medical Advisory BoardAll articles are reviewed for accuracy by our Medical Advisory Board
Educational purpose only • Exercise caution as content is pending human review
Article Review Status
Submitted
Under Review
Approved

Last updated: September 26, 2026 • View editorial policy

Have a follow-up question?

Our Medical A.I. is used by practicing medical doctors at top research institutions around the world. Ask any follow up question and get world-class guideline-backed answers instantly.

Ask Question

Diagnosis: Vitamin B12 Deficiency (Cobalamin Deficiency)

This 72-year-old woman has vitamin B12 deficiency confirmed by the elevated methylmalonic acid (580 nmol/L), despite a low-normal serum B12 level of 210 pg/mL. 1

Diagnostic Reasoning

The clinical picture clearly points to B12 deficiency through the following algorithmic approach:

Step 1: Classify the Anemia by MCV

  • MCV 102 fL = Macrocytic anemia 2, 3
  • This immediately narrows the differential to: vitamin B12 deficiency, folate deficiency, myelodysplastic syndrome, medications (azathioprine, hydroxyurea), hypothyroidism, or alcoholism 2, 3

Step 2: Evaluate Vitamin Levels

  • Folate 12 ng/mL = Normal (rules out folate deficiency)
  • Vitamin B12 210 pg/mL = Low-normal range 1

Critical point: Patients with B12 levels in the low-normal range (200-500 pg/mL) may still be functionally deficient and manifest hematologic, neurologic, or psychiatric symptoms 1. Between 2.2-8% of patients with polyneuropathy have B12 deficiency based on elevated metabolites alone, and 44% of B12-deficient patients have normal serum B12 but abnormal metabolites 4.

Step 3: Confirm with Metabolites

  • Methylmalonic acid 580 nmol/L = ELEVATED (normal <280 nmol/L)
  • This confirms true B12 deficiency 1, 4, 1

Methylmalonic acid is elevated in 98.4% of B12-deficient patients and is more specific than homocysteine (which can be elevated in folate deficiency, pyridoxine deficiency, renal insufficiency, and hypothyroidism) 4.

Step 4: Rule Out Other Causes of Macrocytosis

  • Ferritin 220 ng/mL = Normal (rules out iron deficiency as primary cause) 3
  • The neutrophilia on blood smear may represent a reactive process but does not explain the macrocytic anemia

Important Caveats

The normal MCV does not rule out B12 deficiency. In fact, microcytosis and macrocytosis can coexist (e.g., combined iron and B12 deficiency), neutralizing each other to produce a falsely normal MCV 3. However, this patient has clear macrocytosis at 102 fL.

Folate fortification does not mask macrocytic anemia in B12 deficiency, though high folate supplement use might 1. This patient actually demonstrates the expected pattern: higher folate levels in B12-deficient patients are associated with more severe anemia and cognitive impairment 1.

Underlying Etiology to Investigate

In a 72-year-old woman, the most likely causes are:

  • Pernicious anemia (autoimmune destruction of parietal cells, lack of intrinsic factor) 1
  • Atrophic gastritis with achlorhydria (affects ~15% of adults over 60) 1
  • Malabsorption of food-protein-B12 complex 1

Check anti-intrinsic factor antibodies and anti-parietal cell antibodies to confirm pernicious anemia 5, 6.

Treatment Implications

Initiate parenteral vitamin B12 replacement immediately (1,000 µg intramuscularly, subcutaneously, or intranasally) if pernicious anemia is confirmed or suspected 1. Oral B12 (1,000 µg/day) can be used for other causes of B12 deficiency without malabsorption 1.

The elevated methylmalonic acid definitively establishes the diagnosis and mandates treatment to prevent irreversible neurologic damage, even though the patient's B12 level appears "borderline" 1, 4, 1, 6.

References

2
Guideline

cancer- and chemotherapy-induced anemia.

Journal of the National Comprehensive Cancer Network : JNCCN, 2012

Related Questions

In an 82‑year‑old woman with severe anemia (hemoglobin 7.7 g/dL), what is the significance of a white‑blood‑cell count of 13.4 ×10⁹/L, platelet count of 351 ×10⁹/L, and macrocytic mean corpuscular volume of 103.2 fL, and how should she be managed?
What are the causes of isolated macrocytosis in a 31‑year‑old woman with coeliac disease, persistent elevated antibodies, joint pain, normal hemoglobin, and normal vitamin B12 and folate levels?
What is the appropriate evaluation and initial management for a 51-year-old woman with macrocytic anemia (mean corpuscular volume 100 fL, mean corpuscular hemoglobin 33 pg, red cell distribution width 50.5 %)?
What is the differential diagnosis and recommended work‑up for a 59‑year‑old woman with isolated macrocytosis (mean corpuscular volume 101 fL), normal mean corpuscular hemoglobin concentration, normal red cell distribution width, hemoglobin 12.4 g/dL, hematocrit 39.5 %, and ferritin 86 µg/L?
How should I evaluate and manage a 71-year-old male with macrocytic anemia (red blood cell count 2.23 ×10⁶/µL, hemoglobin 8.3 g/dL, hematocrit 24.9 %, mean corpuscular volume 112 fL, mean corpuscular hemoglobin 37.5 pg)?
How does the skin convert sunlight into vitamin D?
What is the diagnosis for a 17-year-old patient?
How do ashwagandha (Withania somnifera) and melatonin work, and what are the safety considerations when a patient takes both together?
What is the differential diagnosis, including metabolic disorders, for an 8‑day‑old neonate with feeding difficulty, failure to gain weight, regurgitation, and intermittent non‑bilious vomiting without fever?
What is the recommended treatment for an adult with relapsed acute myeloid leukemia after prior midostaurin therapy who has NPM1, FLT3‑ITD, and DNMT3A mutations?
Are there studies comparing the sensitivity and specificity of urinary N‑acetyl‑β‑D‑glucosaminidase (NAG) versus the combined biomarker TIMP‑2·IGFBP7 for early detection of acute kidney injury?

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.