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Test Code BR TOL OV Breath Tolerance Bacterial Overgrowth

Important Note

This test must be scheduled with the Chemistry Laboratory at 206-987-3860. Outside orders should be faxed to 206-985-3124.

Clinical System Name

Breath Tolerance Bacterial Overgrowth


Glucose breath hydrogen


SIBO (Small Intestinal Bacterial Overgrowth)

Lactulose breath hydrogen


This test is to detect bacterial overgrowth and must be scheduled in advance with the Chemistry Lab. (206)987- 3860.  Patients must be off of antibiotics for two weeks and should fast for 12 h prior to test.  A 6 h fast is acceptable for infants. An elevated fasting (baseline) breath sample can be seen with colonic fermentation or bacterial overgrowth.

The ordering provider should specify glucose or lactulose. If glucose is given, the test will last 2 hours; a lactulose challenge will last 3 hours.

Sample Requirements

Specimen: Breath


Preferred Vol:

Minimum Vol:


Note: Diabetic patients will have a fasting blood glucose collected and run before the procedure is started.



STAT Performed TAT
N M, W, Th, day shift 1 d


Test must be scheduled with chemistry lab (206) 987-3860.

Performing Laboratory

Seattle Children's Laboratory    



Department:  Chemistry

Location: Chem East

Phone Number: (206) 987-3860


Reference Range

An interpretation will accompany the report.


Method: Gas Chromatography

Analytical Volume:


CPT Codes


Clinical Utility

Glucose is absorbed in the proximal small bowel. A rise in breath H2/CH4 of >12 ppm over baseline implies bacterial overgrowth in the proximal small bowel.

Lactulose is a non-absorbable sugar that can be used to assess small bowel overgrowth in the proximal and distal small bowel. Bacterial overgrowth will ordinarily cause a biphasic pattern in breath H2. There will be an early response of H2/CH4, with an increase of 12 ppm over the baseline value, followed by a second response which will be very much larger. It is possible that  the two peaks will merge, showing more of an early plateau than a bimodal peak. The second peak, appearing around 3 hours after lactulose administration, will be expected in all patients, with or without bacterial overgrowth. Results should be interpreted in the context of clinical findings. Poor motility will cause an increase in bacteria.

Lack of any H2  or CH4 response throughout the test suggests recent antibiotic use that has eliminated gut bacteria.