Review Question - QID 212750

A 38-year-old woman presents to the clinic complaining of fatigue and recurrent stomach pain for the past 3 years. She reports an intermittent, dull ache at the epigastric region that is not correlated with food intake. Antacids seem to help a little, but the patient still feels uncomfortable during the episodes. She reports that she has been getting increasingly tired over the past week. The patient denies fevers, chills, nausea, vomiting, melena, hematochezia, or diarrhea but does endorse intermittent abdominal bloating. Her past medical history is significant for type 1 diabetes that is currently managed with an insulin pump. Physical examination demonstrates pale conjunctiva and mild abdominal tenderness at the epigastric region. Laboratory studies are shown below:

Leukocyte count: 7,800/mm^3
Segmented neutrophils: 58%
Bands: 4%
Eosinophils: 2%
Basophils: 0%
Lymphocytes: 29%
Monocytes: 7%
Hemoglobin: 10 g/dL
Platelet count:  170,000/mm^3
Mean corpuscular hemoglobin concentration: 36 g/dL
Mean corpuscular volume: 103 µm^3
Homocysteine: 15 mmol/L (Normal = 4.0 – 10.0 mmol/L)
Methylmalonic acid: 0.6 umol/L (Normal = 0.00 – 0.40 umol/L)

What substance would you expect to be decreased in this patient?