Introduction Home testing kits are convenient for both patients and clinicians and can be used in the diagnosis of small intestinal bacterial overgrowth (SIBO), through use of postal Hydrogen and Methane Breath Test (HMBT) kits. This retrospective analysis assessed the validity of home testing and frequency of common issues.

Methods Data from 1518 patients performing lactulose HMBT at home was retrospectively analysed. Patients performed the breath test following AGIP guidelines for preparation and performance. Full written instructions and instructional video were provided and the patients completed the test independently. Samples were analysed using gas chromatography and CO2 was measured as a correction factor to assess sample validity.

Results Of 1518 home tests analysed in 2021, 1445 were performed and analysed successfully (>95%). 73 patients (4.81%) were identified to have issues affecting reliable analysis of the breath test.

Invalid samples – 32 patients produced invalid breath samples at key time points during the test (2.1% of total tests), which may be a result of poor sampling technique or fault with sample collection tube. In 14 of these 32 patients (44%), a diagnosis could be concluded despite the presence of invalid samples. The results of 18 tests could not be determined (1.2% of total tests) and repeat test was recommended. 10 of these patients repeated the test successfully to obtain diagnosis (7 repeated by postal test, 3 repeated in clinic with support from a clinician).

High baseline – 39 tests (2.6% of total tests) were affected by high baseline hydrogen scores, which is a result of poor test preparation or excessive bacterial fermentation and may prevent reliable diagnosis of SIBO. Of these 39, 5 repeated the study following an extended preparatory phase (48-hour low fermentable diet) to attempt to reduce baseline fermentation. Baseline hydrogen scores were reduced in 3 of 5 repeat tests.

Patient error – 2 invalid tests were caused by patient error (0.1% of total tests). These errors included failure to label the sample tubes, and failure to adhere to correct sampling intervals.

Conclusion Hydrogen and Methane Breath Tests can be performed by patients independently at home with >95% success rate. Common issues affecting analysis with home testing are invalid samples (2.1%), and high baseline hydrogen scores preventing reliable diagnosis of SIBO (2.6%). Patient error accounted for 0.1% of total tests performed. Thus, home testing is a viable, safe, and convenient alternative to in-clinic appointments for HMBT.