WBR0173
| Author | [[PageAuthor::Rim Halaby, M.D. [1]]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Pathology |
| Sub Category | SubCategory::Gastrointestinal |
| Prompt | [[Prompt::A 28 year old female patient presents to the physician's office complaining of excessive fatigue and pallor. Following appropriate work-up, the diagnosis of megaloblastic anemia with low vitamin B12 levels. The patient is then instructed to drink radiolabeled vitamin B12 and undergo a single vitamin B12 intramuscular injection 1 hour later. The next day, the patient's urinalysis shows more than 10% radiolabeled vitamin B12 detected in the urine. What is the most likely diagnosis?]] |
| Answer A | AnswerA::Pernicious anemia |
| Answer A Explanation | AnswerAExp::Schilling test is normal in pernicious anemia only when intrinsic factor is added. |
| Answer B | AnswerB::Bacterial overgrowth syndrome |
| Answer B Explanation | AnswerBExp::Schilling test is normal in bacterial overgrowth syndrome only when antibiotics are added. |
| Answer C | AnswerC::Pancreatitis |
| Answer C Explanation | AnswerCExp::Schilling test is normal in pancreatitis only when pancreatic enzymes are added. |
| Answer D | AnswerD::Low vitamin B12 intake |
| Answer D Explanation | AnswerDExp::Schilling test is normal in low intake of vitamin B12 when oral and IM injections of vitamin B12 are given. |
| Answer E | AnswerE::Malabsorption |
| Answer E Explanation | AnswerEExp::In malabsorption, schilling test is abnormal even after addition of all the aforementioned elements. |
| Right Answer | RightAnswer::D |
| Explanation | [[Explanation::The test described in this vignette is the Schilling test. It is multi-step test that appropriately diagnoses the etiology of low vitamin B12 levels. At first, the patient is given oral radiolabeled vitamin B12 followed by intramuscular (IM) injections of unlabeled vitamin B12. The IM injections will saturate the hepatic receptors of vitamin B12 to ensure that oral radiolabeled vitamin B12 is excreted in the urine once absorbed in the GI tract. If oral radiolabeled vitamin B12 is found in more than 10% in the urine the next day, the diagnosis of vitamin B12 deficiency due to low intake is diagnosed. If the vitamin B12 levels are less than 10% in the urine the next day, further work-up is required. Then the test is repeated while adding intrinsic factor (IF). If urinary vitamin B12 levels are normal, the diagnosis of pernicious anemia is made. Further work-up includes the addition of antibiotics and pancreatic enzymes to rule out bacterial overgrowth syndrome and pancreatitis, respectively. Finally, patients with malabsorption will remain to have low urinary vitamin B12 levels, even when all the above elements are added.
Educational Objective: A normal schilling test after the addition of oral radiolabeled vitamin B12 and intramuscular injections of vitamin B12 is diagnostic of decreased vitamin B12 intake. Reference:
Zuckier LS, Chervu LR. Schilling evaluation of pernicious anemia: current status. J Nucle Med. 1984; 25(9):1032-9 |
| Approved | Approved::No |
| Keyword | WBRKeyword::oral, WBRKeyword::intramuscular, WBRKeyword::vitamin, WBRKeyword::B12, WBRKeyword::cobalamin, WBRKeyword::injection, WBRKeyword::injections, WBRKeyword::megaloblastic, WBRKeyword::anemia, WBRKeyword::fatigue, WBRKeyword::pallor, WBRKeyword::schilling, WBRKeyword::Schilling, WBRKeyword::test, WBRKeyword::work, WBRKeyword::up, WBRKeyword::work-up |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |