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
Explanation
This child has lactose intolerance due to lactose malabsorption, suggested by the characteristic relationship between dairy ingestion and gastrointestinal symptoms.
The key clinical features are:
Abdominal pain, bloating and flatulence occurring after milk or ice cream consumption
Watery diarrhea following lactose ingestion
Improvement when dairy products are avoided
Normal growth and weight gain, arguing against significant chronic malabsorptive disease
Acidic stool pH (5.0) and positive reducing substances, supporting carbohydrate malabsorption
Negative tissue transglutaminase IgA, making celiac disease less likely in this clinical context
Lactose is normally hydrolyzed in the small intestine by lactase into glucose and galactose. When lactase activity is insufficient, unabsorbed lactose reaches the colon, where it is fermented by intestinal bacteria. This produces hydrogen and other gases, while the unabsorbed carbohydrate increases the osmotic load in the intestine, resulting in bloating, abdominal discomfort and watery diarrhea.
Most appropriate diagnostic test
B. Hydrogen breath test after an oral lactose load is the most appropriate confirmatory test among the options.
After lactose administration, an increase in breath hydrogen indicates that lactose has reached the colon and has been fermented by bacteria. The test is non-invasive and is widely used in children to demonstrate lactose malabsorption. Importantly, the diagnosis of clinically significant lactose intolerance is strengthened when the characteristic gastrointestinal symptoms occur during the test.
The ESPGHAN position paper describes hydrogen breath testing as an established diagnostic approach for carbohydrate malabsorption in children. A rise in breath hydrogen of >20 ppm above baseline is generally considered evidence of lactose malabsorption.
Why the other options are incorrect
A. Duodenal biopsy demonstrating villous atrophy — Incorrect
Duodenal biopsy is used when evaluating celiac disease, particularly when histological confirmation is required. Villous atrophy is not a feature of isolated lactose intolerance. Furthermore, this child’s negative tTG-IgA and absence of growth failure make celiac disease less likely.
C. Measurement of fecal elastase — Incorrect
Fecal elastase is used to assess exocrine pancreatic insufficiency. Low fecal elastase may occur in conditions such as cystic fibrosis or chronic pancreatic disease. It does not diagnose lactose malabsorption.
D. Serum anti-endomysial antibody testing — Incorrect
Anti-endomysial antibody (EMA-IgA) is another highly specific serological test for celiac disease. It does not evaluate lactose digestion or absorption.
E. Sweat chloride test — Incorrect
The sweat chloride test is used to diagnose cystic fibrosis. Cystic fibrosis can cause chronic diarrhea and malabsorption through pancreatic insufficiency, but the characteristic post-dairy symptoms in this child, normal growth and evidence of carbohydrate malabsorption point toward lactose malabsorption instead.
Important distinction: lactose malabsorption vs lactose intolerance
These terms should not be used interchangeably:
Lactose malabsorption = inadequate digestion/absorption of lactose.
Lactose intolerance = gastrointestinal symptoms resulting from lactose malabsorption.
Therefore, a positive hydrogen breath test demonstrates lactose malabsorption, while reproduction of the child’s typical symptoms during testing helps establish clinically relevant lactose intolerance.
High-Yield Exam Pearl
Symptoms after milk + bloating/flatulence + watery diarrhea + acidic stool → think lactose malabsorption.
Hydrogen breath test after lactose administration → confirms lactose malabsorption and, when typical symptoms are reproduced, supports lactose intolerance.
References
- Broekaert IJ, Anderson SE, Amil Dias J, et al. An ESPGHAN position paper on the use of breath testing in paediatric gastroenterology. J Pediatr Gastroenterol Nutr. 2022;74(1):96-117
- Heyman MB; Committee on Nutrition. Lactose intolerance in infants, children, and adolescents. Pediatrics. 2006;118(3):1279-1286.
You can also practice more high yield clinical scenario based MCQs on Gastrointestinal System.
