Additional Detail:

Background
Breath testing is now the predominant method to evaluate patients for potential overgrowth because of its simplicity, safety, and lack of invasiveness. These methods all rely on the modification of a substrate by bacteria. The substrate most commonly used is a readily metabolized carbohydrate, such as lactulose, glucose, sucrose, or xylose.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3099351/

All breath tests rely on the recovery and quantification of an exhaled gas produced by the bacterial metabolism of the ingested substrate. The development of inexpensive, commercially available gas chromatographs to measure exhaled hydrogen and/or methane has led to the widespread use of breath testing for the diagnosis of bacterial overgrowth.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3099351/

Preparation:
Up to four weeks before the test, certain activities should be avoided https://pubmed.ncbi.nlm.nih.gov/24095975/:

• Avoidance of antibiotics for 4 weeks before testing
• Avoidance of colonic purging within 4 weeks of testing
• Avoidance of bismuth for 2–4 weeks before testing
• Avoidance of probiotics for 2–4 weeks before testing
• Avoidance of prokinetics for 3 half-lives before testing
• Consumption of a diet free of nonabsorbable carbohydrates (pasta, bread, fiber cereal, beans) the evening before testing
• Overnight fast before testing
• Avoid cigarette smoking before and during testing
• Consider mouthwash with chlorhexidine solution before substrate ingestion

Process
The test takes 3-4 hours, beginning with the ingestion of some sugar (e.g., lactulose or glucose); and breath samples are taken every 15-30 minutes.

Diagnosis
If certain thresholds are met, the test is considered positive.

There is much variance on what constitutes a positive test https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3155069/, but an example criteria is:

• hydrogen that increases >= 20ppm above the baseline level
• methane level of >= 10ppm at any time during the test

Downsides
Studies have been mixed on the sensitivity with ranges between 17% and 68%. https://pubmed.ncbi.nlm.nih.gov/24095975/

Condition-Specific Notes:

Some breath tests use different sugars (e.g. lactose, lactulose, glucose, fructose)

Type:

labs