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Difficulty: EasyHematology and Oncology

A 68-year-old man presents to his primary care physician reporting progressive fatigue, generalized weakness, and a persistent "tingling" sensation in both of his feet that began four months ago. He has a history of type 2 diabetes mellitus, which is currently managed with metformin. His vital signs are within normal limits. Physical examination demonstrates pale conjunctivae, a smooth and erythematous tongue, and decreased vibratory sensation in the bilateral lower extremities. Laboratory analysis reveals a hemoglobin of 9.6 g/dL, a mean corpuscular volume of 115 fL, a white blood cell count of 4,500/mm³, and a platelet count of 140,000/mm³. Which of the following is the most appropriate next step in the diagnostic workup for this patient?

  1. Assessment of serum cobalamin and folic acid concentrationsAnswer
  2. B
    Iron panel including transferrin saturation
  3. C
    Empiric trial of oral ferrous sulfate
  4. D
    Diagnostic bone marrow evaluation
  5. E
    Genetic testing for globin chain mutations

Answer

Assessment of serum cobalamin and folic acid concentrations
The correct answer identifies that the initial diagnostic step for a patient with macrocytic anemia (MCV > 100 fL) is to check cobalamin (vitamin B12) and folate levels. This patient's presentation of macrocytosis, glossitis, and peripheral neuropathy (decreased vibratory sensation) in the setting of long-term metformin use (which can interfere with B12 absorption in the terminal ileum) is highly classic for vitamin B12 deficiency.

Step-by-Step Solution

1
Analyze the patient's complete blood count results.
The patient has anemia (hemoglobin 9.6 g/dL) with macrocytosis (mean corpuscular volume 115 fL).
Identifying the morphological classification of anemia (microcytic, normocytic, or macrocytic) narrows down the differential diagnosis.
2
Correlate the laboratory findings with the clinical presentation.
Macrocytic anemia paired with peripheral neuropathy (tingling, decreased vibratory sensation) and glossitis strongly suggests vitamin B12 deficiency.
Neurologic deficits are a hallmark distinguishing feature of vitamin B12 (cobalamin) deficiency compared to folate deficiency, though both cause macrocytic anemia.
3
Determine the appropriate diagnostic test to confirm the clinical suspicion.
Checking serum levels of vitamin B12 (cobalamin) and folate is the initial non-invasive step.
Definitive diagnosis requires biochemical evidence of the vitamin deficiency before initiating lifelong therapy or more invasive testing.

Key Concept

The initial evaluation of a patient presenting with macrocytic anemia and neurologic symptoms requires measuring serum cobalamin (vitamin B12) and folate levels.
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Topics

Hematology and Oncology

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