WBR1117

Author	[[PageAuthor::Mugilan Poongkunran M.B.B.S [1]]]
Exam Type	ExamType::USMLE Step 3
Main Category	MainCategory::Primary Care Office
Sub Category	SubCategory::Gastrointestinal
Prompt	[[Prompt::An 18 year old male come to the office for periodic abdominal cramps. The abdominal cramp typically starts after having his meals and is associated with flatulence and non bloody diarrhea sometimes. These episodes are more often associated with intake of dairy products. Otherwise his past history is insignificant. His family history is remarkable for lactose intolerance in his mother. He does not smoke and does not consume alcohol. On examination his vitals are normal. All system examinations are normal. Which of the following would be the next step in the management of this patient?]]
Answer A	AnswerA::Lactose tolerance test
Answer A Explanation	AnswerAExp::Lactose tolerance test has a sensitivity and specificity inferior to the breath hydrogen test and hence usually not preferred.
Answer B	AnswerB::Lactose breath hydrogen test
Answer B Explanation	AnswerBExp::The breath hydrogen test is simple and noninvasive test that has a sensitivity and specificity superior to the absorption test and hence usually preferred.
Answer C	AnswerC::Genetic test for primary lactose malabsorption
Answer C Explanation	AnswerCExp::Genetic test for primary lactose malabsorption is very expensive and hence not done routinely.
Answer D	AnswerD::Small bowel biopsy
Answer D Explanation	AnswerDExp::Small bowel biopsy cannot necessarily establish the diagnosis of disaccharidase deficiency.
Answer E	AnswerE::Large bowel biopsy
Answer E Explanation	AnswerEExp::Large bowel biopsy cannot necessarily establish the diagnosis of disaccharidase deficiency and the pathology lies in the small intestine.
Right Answer	RightAnswer::B
Explanation	[[Explanation::Lactose intolerance is characterized by low intestinal lactase levels, which may be due to reduced genetic expression of the enzyme lactase-phlorizin hydrolase or due to mucosal injury. The symptoms include diarrhea, abdominal pain, and flatulence after ingestion of milk or milk-containing products. The condition can be confirmed by a test of absorption (eg, lactose absorption test) or malabsorption (lactose breath hydrogen test). The breath hydrogen test is simple and noninvasive test that has a sensitivity and specificity superior to the absorption test and hence usually preferred. The test is done in the fasting state, and oral lactose is given at a usual dose of 2 g/kg (maximum dose, 25 g). Breath hydrogen is sampled at baseline and at 30-minute intervals after the ingestion of lactose for three hours. The post-lactose and baseline values are compared. A breath hydrogen value of 10 ppm (parts per million) is considered as as normal and values over 20 ppm are considered diagnostic of lactose malabsorption. Educational Objective: Lactose intolerance is diagnosed through proper history and lactose breath hydrogen test References: ]]
Approved	Approved::Yes
Keyword	[[WBRKeyword::Lactose intolerance]]
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