All Sample Questions

Vitamin B12 Deficiency 1

Vitamin B12 deficiency


Vignette: A 65-year-old man presents to his primary care physician for a routine check-up. He mentions that he has been experiencing progressive weakness and fatigue for the past several months. On physical examination, pallor is noted. Complete blood count (CBC) reveals a hemoglobin of 9.5 g/dL, hematocrit of 28%, and a mean corpuscular volume (MCV) of 110 fL. Serum vitamin B12 and folate levels are within normal limits. A peripheral blood smear is obtained and reveals hypersegmented neutrophils and macro-ovalocytes. Which of the following is the most likely cause of this patient's anemia?


A) Iron deficiency

B) Vitamin B12 deficiency

C) Folate deficiency

D) Sideroblastic anemia

E) Thalassemia


C) Folate deficiency


The patient's clinical presentation and laboratory findings are consistent with macrocytic anemia, which is characterized by an MCV >100 fL. The peripheral blood smear findings of macro-ovalocytes and hypersegmented neutrophils are classic for megaloblastic anemia, a subtype of macrocytic anemia. The most common causes of megaloblastic anemia are vitamin B12 and folate deficiencies. However, this patient's vitamin B12 levels are normal, making folate deficiency the most likely cause. Folate deficiency can result from poor dietary intake (common in the elderly), malabsorption, or increased demand (e.g., pregnancy). It can also be seen in chronic alcoholism and in patients taking certain medications (e.g., phenytoin, methotrexate, sulfonamides). Unlike vitamin B12 deficiency, folate deficiency does not cause neurologic symptoms.


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