WBR0173
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| Author | [[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Alison Leibowitz) (Reviewed by Serge Korjian)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Pathology |
| Sub Category | SubCategory::Gastrointestinal |
| Prompt | [[Prompt::A 28-year-old woman presents to the physician's office with complaints of excessive fatigue and pallor. Following appropriate work-up, you diagnose her with megaloblastic anemia, with low vitamin B12 levels. As part of her work-up, the patient is instructed to drink a preparation containing radio-labeled vitamin B12. One hour later, she receives a second dose of vitamin B12 as an intramuscular injection. Over the next 24 hours, the patient collects her urine for analysis which shows more 35% radioactive vitamin B12 by radiotelegraph. What is the most likely diagnosis in this patient?]] |
| Answer A | AnswerA::Pernicious anemia |
| Answer A Explanation | [[AnswerAExp::Schilling test results are normal in pernicious anemia only when intrinsic factor is added.]] |
| Answer B | AnswerB::Bacterial overgrowth syndrome |
| Answer B Explanation | [[AnswerBExp::Schilling test results are normal in bacterial overgrowth syndrome only when antibiotics are added.]] |
| Answer C | AnswerC::Pancreatitis |
| Answer C Explanation | [[AnswerCExp::Schilling test results are normal in pancreatitis only when pancreatic enzymes are added.]] |
| Answer D | AnswerD::Low vitamin B12 intake |
| Answer D Explanation | [[AnswerDExp::Schilling test results are normal in low intake of vitamin B12, when oral and IM injections of vitamin B12 are administered.]] |
| Answer E | AnswerE::Malabsorption |
| Answer E Explanation | [[AnswerEExp::In cases of malabsorption, Schilling test results are abnormal even following the addition of all the aforementioned elements.]] |
| Right Answer | RightAnswer::D |
| Explanation | [[Explanation::This scenario closely describes the Schilling test procedure. The Schilling test is used in the setting of megaloblastic anemia and low vitamin B12 levels to diagnose the etiology of the vitamin deficiency. At first, the patient is given oral radio-labeled vitamin B12, followed by an intramuscular (IM) injection of unlabeled vitamin B12. The IM injections saturate the hepatic receptors of vitamin B12, to ensure that, once absorbed by the GI tract, the oral radio-labeled vitamin B12 will be excreted in the urine. If oral radio-labeled vitamin B12 is detected as more than 10% in the urine the following day, the patient is diagnosed with vitamin B12 deficiency due to low intake. If the vitamin B12 levels are less than 10% in the urine the following day, further work-up is required. If this occurs, the Schilling test is repeated while adding intrinsic factor (IF). If urinary vitamin B12 levels are normal, the patient is diagnosed with pernicious anemia. Further work-up includes the addition of antibiotics and pancreatic enzymes to rule out bacterial overgrowth syndrome and pancreatitis, respectively. Patients with malabsorption will have low urinary vitamin B12 levels, even following the administration of all the above elements. Educational Objective: A Schilling test after the addition of oral radiolabeled vitamin B12 and intramuscular injections of vitamin B12, with normal results, is diagnostic of decreased vitamin B12 intake. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Vitamin, WBRKeyword::Vitamin B12, WBRKeyword::B12, WBRKeyword::Cobalamin, WBRKeyword::Injection, WBRKeyword::Megaloblastic anemia, WBRKeyword::Macrocytic anemia, WBRKeyword::Anemia, WBRKeyword::Schilling test, WBRKeyword::Schilling, WBRKeyword::Intrinsic factor, WBRKeyword::Pernicious Anemia, WBRKeyword::Malabsorption |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |