This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Stomach & Duodenum, Subject name: Surgery
A 58-year-old woman has a gastric ulcer, achlorhydria, and vibration sense loss in the lower extremities. She has a megaloblastic anemia. What test would help support a diagnosis of pernicious anemia? 
Select and explain. 
A. Response to injection of radioactive B12, B. Endoscopic retrograde cholangiopancreatography (ERCP), C. Prothrombin time (PT), D. Radiolabeled B12 given orally
D: Radiolabeled B12 given orally
Answer: D: Radiolabeled B12 given orally 
Explanation: The Schilling test is performed by giving radiolabeled B12 orally (after saturating the B12 stores by intramuscular B12 ). In pernicious anemia, less than 3% of the label is found in the 24-hour urine collection (N>7%). Hemoglobin electrophoresis will detect defects in a- or b-globin chain synthesis, as seen in thalassemia (Mediterranean anemia).