What is the procedure for a hydrogen breath test (HBT) for diagnosing lactose intolerance?

Hydrogen Breath Test Procedure for Lactose Intolerance

The hydrogen breath test for lactose intolerance involves ingestion of 25-50g lactose dissolved in 200-500ml water after an overnight fast, followed by collection of end-expiratory breath samples at 15-30 minute intervals for three hours, with a rise in hydrogen concentration above baseline by more than 20 parts per million indicating a positive diagnosis. 1

Preparation for the Test

• Patient must fast overnight (8-12 hours) before the test
• Avoid antibiotics for 2-4 weeks prior to testing
• Avoid laxatives and fiber supplements for 24 hours before the test
• Avoid smoking and vigorous exercise on the day of the test
• Brush teeth thoroughly before the test to minimize oral bacteria

Test Procedure

Step 1: Baseline Measurement

• Collect baseline (0 minute) breath sample before lactose ingestion
• This establishes the patient's baseline hydrogen level

Step 2: Lactose Challenge

• Administer 25-50g of lactose dissolved in 200-500ml of water 1
• Standard adult dose is typically 25g (equivalent to 500ml of milk)

Step 3: Breath Sample Collection

• Collect end-expiratory breath samples at 15-30 minute intervals for three hours 1
• Most critical sampling points are at:
  • 0 minutes (baseline)
  • 120 minutes (2 hours)
  • 180 minutes (3 hours)

Step 4: Hydrogen Measurement

• Analyze breath 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 1
• A positive result indicates lactose malabsorption
• Note: Due to a false negative rate of up to 25%, a negative result does not exclude the diagnosis 1
• Some patients may also produce methane rather than hydrogen, which should be measured when available 2

Important Considerations

Test Accuracy

• Sensitivity of the test varies depending on sampling protocol
• A two-sample test (0 min and 120 min) has a high false-negative rate of 33.4% 3
• A three-sample test (0 min, 120 min, and 180 min) improves accuracy with only 5.9% false-negative rate 3

Symptom Correlation

• Record symptoms during the test (nausea, abdominal pain, borborygmi, bloating, diarrhea)
• Symptom intensity is typically higher in those with positive tests 4
• Bloating has the highest sensitivity (70%) while diarrhea has the highest specificity (90%) 4

Hydrogen Non-Excreters

• Approximately 18% of patients may be hydrogen non-excreters 5
• In these cases, methane measurement can be valuable, as 6% of patients may be positive for methane only 2

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 6
• Symptom diary: Track symptoms in relation to dairy consumption 6
• Genetic testing: Testing for lactase-persistent alleles (LCT-13,910 C/T) may be useful in certain populations 6

Post-Test Management

• For positive tests, consider lactase supplements before consuming dairy products
• Most people with lactose intolerance can gradually reintroduce small amounts of dairy (up to 12 oz milk daily) 6
• Consider lactose-free alternatives to maintain adequate calcium intake

Remember that a negative test with persistent symptoms warrants consideration of a lactose-free diet trial, as false negatives can occur in up to 25% of cases 1.