Patient preparation to minimize fasting breath hydrogen:
(1) 12 hour fast after an evening meal consisting of meat and rice.
(2) Foods high in unabsorbable carbohydrates are avoided the evening before.
Criteria for bacterial overgrowth of the small intestine - both of the following:
(1) high fasting breath hydrogen level (> 15 parts per million) after dietary preparation on at least one occasion
(2) an increase in breath hydrogen >= 12 parts per million (ppm) within 2 hours of a 50 gram glucose load
where:
• Only a small subset of patients with bacterial overgrowth have a persistently high fasting breath hydrogen level.
• The increase in breath hydrogen after the glucose load is a good screening test for bacterial overload.
Performance (page 987):
• The presence of both criteria is specific for bacterial overgrowth but insensitive.
• A high fasting breath hydrogen is specific but insensitive.
• A false positive fasting breath hydrogen test may occur if a patient does not adhere to the preparation instructions.
• False positive breath tests may occur in patients with rapid gastric emptying and intestinal transit to the cecum.
• False negative breath tests may occur in a patient treated with antibiotics.
• False negative breath tests can occur if the pH of the colonic contents is too low.
