Clinical Scenario:
A 6-year-old boy presents with recurrent abdominal pain, bloating, flatulence, and watery diarrhea for the past 3 months. His symptoms typically occur 1–2 hours after consuming milk or ice cream and improve when dairy is avoided. There is no weight loss, no blood in stool, and growth parameters are normal. Physical examination is unremarkable.
Stool examination shows acidic pH (5.0) and positive reducing substances. Tissue transglutaminase IgA is negative.
Which of the following is the most appropriate diagnostic test to confirm the suspected condition?
A. Duodenal biopsy demonstrating villous atrophy
B. Hydrogen breath test after oral lactose load
C. Measurement of fecal elastase
D. Serum anti-endomysial antibody testing
E. Sweat chloride test
Correct answer & Explanation:
Correct answer: Hydrogen breath test after lactose load
Discussion: Lactose Intolerance
Lactose intolerance is characterized by:
Post-dairy abdominal symptoms
Normal growth (rules out chronic malabsorption)
Acidic stool with reducing substances (carbohydrate malabsorption)
The hydrogen breath test is the gold standard non-invasive diagnostic test. In lactose intolerance, undigested lactose is fermented by colonic bacteria, producing hydrogen, which is measured in expired air.
Why others are incorrect:
Duodenal biopsy → for celiac disease
Fecal elastase → for pancreatic insufficiency
Anti-endomysial antibodies → for celiac disease
Sweat chloride test— cystic fibrosis
