Kerlin and Wong evaluated breath hydrogen testing to diagnose a patient with bacterial overgrowth of the small intestine. This can help avoid the problems associated with radio-labelled carbohydrates and make testing more accessible. The authors are from Princess Alexandra Hospital in Brisbane, Australia.


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



• 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.


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