Evaluation of Test Results

Diagnostic Criteria

End-expiratory hydrogen and methane are measured by gas chromatography at baseline and periodically for 2 hours after 10 grams of lactulose are ingested. The diagnostic criteria for a positive SIBO result is a rise above baseline of 20 parts per million (hydrogen and methane) prior to the 90 minute breath collection.

Causes of False-Negative Results

False-negative results are reported in 5-18% bacterial overgrowth tests. There are various reasons for false-negative results. Some patients possess bacteria that produce neither hydrogen nor methane. However, the major cause for false-negative results is poor patient preparation. Administration of antibiotics within 4 weeks of testing sterilizes the colon to reduce bacterial colony counts. Laxatives and enemas can also decrease hydrogen and methane responses. Hydrogen and methane production can decrease with severe diarrhea that changes colonic pH.

Causes of False-Positive Results

False-positive results are almost always the result of improper test preparation or conduct. Patients need to avoid foods with high fiber content 24 hours prior to the test. If patients consume foods with fiber, they will have high hydrogen or methane levels being produced during the test. Cigarette smoke contains hydrogen gas. If patients smoke prior to the test, a false test result may result. Sleeping during the test can delay gastric emptying and slow down the removal of hydrogen from the blood.