Hydrogen Breath Test Procedure for Lactose Intolerance
The hydrogen breath test for lactose intolerance involves an overnight fast, ingestion of 25-50g lactose dissolved in water, and collection of end-expiratory breath samples at 15-30 minute intervals for three hours, with a rise in hydrogen concentration above 20 parts per million indicating a positive diagnosis. 1
Preparation for the Test
- Patient should fast overnight (8-12 hours) before the test
- Avoid antibiotics for 2-4 weeks prior to testing
- Avoid laxatives and colonoscopy preparation for at least 1 week before testing
- No smoking on the day of the test
- No sleeping during the test (may affect breath hydrogen production)
- No vigorous exercise during the test
Test Procedure
Baseline sample collection:
- Collect end-expiratory breath sample before lactose ingestion (0 minute)
- This establishes baseline hydrogen levels
Lactose challenge:
- Administer 25-50g lactose dissolved in 200-500ml water
- Standard adult dose is typically 25g (equivalent to 500ml milk)
- Pediatric dosing may be weight-adjusted
Serial breath sampling:
- Collect end-expiratory breath samples at 15-30 minute intervals for 3 hours
- Critical sampling points: 0,60,90,120,150, and 180 minutes
- The 120-minute sample is particularly important as all positive tests show elevated H₂ at this timepoint 2
Breath analysis:
- Analyze samples using an electrochemical cell or gas chromatography
- Record hydrogen concentration in parts per million (ppm)
Interpretation of Results
- Positive test: Rise in hydrogen concentration >20 ppm above baseline
- Negative test: No significant rise in hydrogen concentration
Important Considerations
- False negative rate of up to 25% exists, so a negative result does not exclude lactose intolerance 1
- Consider measuring methane in addition to hydrogen, as some patients (approximately 6%) may be hydrogen non-producers but methane producers 3
- Hydrogen non-excretion occurs in up to 20% of tested subjects, which can affect test accuracy 4
- A three-sample test (0 min, 120 min, and 180 min) provides good sensitivity while reducing testing burden 5
Symptom Assessment During Testing
- Record symptoms during the test: nausea, abdominal pain, borborygmi, bloating, and diarrhea
- Symptom development correlates with breath test results:
- Bloating has highest sensitivity (70%)
- Diarrhea has highest specificity (90%) 6
- The presence of multiple symptoms increases the likelihood of a positive test
Alternative Diagnostic Approaches
If breath testing is unavailable or inconclusive:
- Elimination trial: Remove lactose from diet for 2 weeks, then reintroduce to observe symptom recurrence 7
- Genetic testing: Testing for lactase-persistent alleles (LCT-13,910 C/T) may be useful in certain populations 7
Post-Test Recommendations
- If positive, consider a trial of lactose-free diet or lactase supplements
- Even with a negative test, if symptoms strongly suggest lactose intolerance, consider a dietary elimination trial 1
- Most people with lactose intolerance can tolerate small amounts of dairy (up to 12 oz milk daily) 7
Remember that symptoms alone are not sufficient for diagnosis, as they overlap with other conditions like irritable bowel syndrome. The hydrogen breath test provides objective evidence of lactose malabsorption to guide appropriate management.