WBR0173

Author	[[PageAuthor::Rim Halaby, M.D. [1], Alison Leibowitz [2] (Reviewed by Alison Leibowitz)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pathology
Sub Category	SubCategory::Gastrointestinal
Prompt	[[Prompt::A 28-year-old female presents to the physician's office with complaints of excessive fatigue and pallor. Upon appropriate work-up, you diagnose her with megaloblastic anemia, with low vitamin B12 levels. You instruct the patient to drink radio-labeled vitamin B12 and undergo a single vitamin B12 intramuscular injection that day. The following day, the patient's urinalysis detects more than 10% radiotelegraph vitamin B12 in the urine. Which of the following diagnosis is most likely given to 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::In this scenario, the patient undergoes the Schilling test. The Schilling test is a multi-step test, which appropriately diagnoses the etiology of low vitamin B12 levels. At first, the patient is given oral radio-labeled vitamin B12, followed by intramuscular (IM) injections 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. References: Zuckier LS, Chervu LR. Schilling evaluation of pernicious anemia: current status. J Nucle Med. 1984; 25(9):1032-9]]
Approved	Approved::Yes
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
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