A test is only worth doing if the result would change what you do next. The gut tests below differ enormously in what they measure, how reliable they are, and whether the NHS offers them - and the most marketed tests are often the least validated. Here is what each one actually shows.
| Test | What it looks for | Strengths & limits | UK access |
|---|---|---|---|
| Hydrogen/methane breath test | SIBO and methane overgrowth (IMO) | Non-invasive; standardised cut-offs exist, but lactulose tests often reflect transit and produce false positives | Not in the NICE IBS pathway; some gastro clinics and many private labs |
| Comprehensive stool analysis | Microbiome balance, pathogens, inflammation markers (e.g. faecal calprotectin) | Calprotectin is genuinely useful to flag inflammation; “dysbiosis” panels are harder to act on | Calprotectin on NHS; full panels usually private |
| Faecal elastase | Exocrine pancreatic insufficiency | Simple, validated; cheap and decisive when the clue fits | Available on the NHS |
| SeHCAT scan | Bile acid malabsorption | The reference test; under-used despite a clear treatment | NHS, by gastroenterology referral |
| Organic acids test (OAT) | Marketed as a “candida marker” (D-arabinitol) | Limited validation - mainly studied in invasive candidiasis in immunocompromised patients; weak basis for diagnosing gut candida | Private only |
| Small-bowel (duodenal) aspirate | SIBO and SIFO directly, by culture | Closest thing to a gold standard; invasive (done at endoscopy) | Specialist NHS or private, selected cases |
Ordering every test rarely helps; it produces incidental findings that send you down the wrong path. The better approach is to match the test to the strongest clue in your story - greasy stools point to elastase, urgent post-meal diarrhoea after gallbladder surgery points to SeHCAT, bloating that began after food poisoning points to a breath test. The conditions library maps clues to investigations.
The single most important caveat: a positive test is not the same as a cause. Breath tests can be positive because of fast transit; stool cultures can grow organisms that are simply normal residents. Results inform a clinical picture - they don’t replace one.
For the two tests people ask about most, see how breath testing is interpreted in the SIBO guide, and why candida testing is so often misleading in the candida guide. If you’re deciding whether testing is worth it at all, read Is it IBS or SIBO?
Unsure which test is worth your money?
Enquire about a consultation