Review Question - QID 212388

This patient with anemia, elevated mean corpuscular volume, and neurological deficits most likely has vitamin B12 deficiency, which would present with high methylmalonic acid and high homocysteine levels.

Vitamin B12 deficiency causes anemia because it leads to decreased DNA synthesis with normal RNA and protein synthesis. Under normal metabolic conditions, vitamin B12 reserves will last several months, so B12 deficiency will only result after an extended time course. Bariatric surgery can result in late B12 deficiency because it can remove the production site of intrinsic factor that is required for B12 absorption. Notably, vitamin B12 deficiency will present with a macrocytic anemia with hypersegmented neutrophils on peripheral blood smear. It can be distinguished from folate deficiency by the associated neurologic deficits such as decreased vibratory sensation and spastic paresis. In addition, vitamin B12 can be identified by high serum methylmalonic acid and homocysteine levels.

Incorrect Answers:
Answer 1: Elevated bilirubin levels would be seen in extrinsic hemolytic anemias; however, this patient's symptoms are more consistent with vitamin B12 deficiency given the elevated mean corpuscular volume.

Answer 3: High transferrin levels would be seen in iron deficiency anemia; however, this patient's symptoms are more consistent with vitamin B12 deficiency given the elevated mean corpuscular volume.

Answer 4: Low haptoglobin levels would be seen in intrinsic hemolytic anemia; however, this patient's symptoms are more consistent with vitamin B12 deficiency given the elevated mean corpuscular volume.

Answer 5: Normal methylmalonic acid and high homocysteine levels would be seen in folate deficiency, however, this patient's symptoms are more consistent with vitamin B12 deficiency given the associated neurological symptoms.

Bullet Summary:
Vitamin B12 deficiency causes an anemia with high methylmalonic acid and high homocysteine levels.