Lactose Intolerance 1. Background Definition: Inability to…
Lactose Intolerance 1. Background Definition: Inability to digest lactose, the main carbohydrate in milk and dairy products, due to lactase enzyme deficiency in the brush border of the small intestine. Pathophysiology: Undigested lactose remains in the intestinal lumen → osmotic diarrhea and bacterial fermentation → gas, bloating, and cramping. Types: Primary (genetic): Gradual loss of lactase after childhood (most common worldwide). Secondary (acquired): Due to mucosal injury (celiac disease, gastroenteritis, Crohn disease). Congenital: Rare, autosomal recessive, presents in infancy. Epidemiology: Very common globally; affects up to 90% of Asian, African, and Native American populations; less common in Northern Europeans. 2. History Symptoms: Bloating, flatulence, crampy abdominal pain, and watery diarrhea after ingestion of milk or dairy products. Symptoms occur 30 minutes to 2 hours after lactose ingestion. Risk factors: Increasing age, certain ethnic backgrounds, recent intestinal infection, or small bowel disease. Relief: Avoidance of dairy eliminates symptoms. 3. Exam Findings Usually benign; may show mild abdominal distension or hyperactive bowel sounds. Signs of dehydration if diarrhea severe. Otherwise normal physical exam. 4. Making the Diagnosis Gold standard: Hydrogen breath test — elevated breath hydrogen after lactose load indicates malabsorption. Common alternative: Lactose elimination and re-challenge — symptom resolution after lactose avoidance confirms diagnosis. Supportive tests: Stool acidity test (infants): Low stool pH due to fermentation. Small bowel biopsy: Rarely needed; shows decreased lactase activity (used to rule out secondary causes). 5. Management A. Dietary Lactose restriction or use of lactose-free dairy products. Many patients tolerate small amounts of milk with meals. B. Supplements Lactase enzyme replacement before dairy intake (e.g., Lactaid). Calcium and vitamin D supplementation to prevent deficiency in those avoiding dairy. C. Treat underlying cause (if secondary) Address intestinal mucosal disease (e.g., celiac disease, Crohn disease, gastroenteritis recovery). A 23-year-old woman reports several months of bloating, flatulence, and crampy abdominal pain that occur about 1 hour after drinking milk or eating ice cream. She denies fever, weight loss, or blood in her stool. Physical examination is normal. Which of the following is the most appropriate diagnostic test to confirm lactose intolerance?
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