An IBS diagnosis is made by exclusion: serious disease is ruled out, the remaining symptoms are named, and management begins. That is appropriate - but it means the work-up stops before it reaches the conditions below, several of which are testable and treatable. Here is the library, with the two most fully developed guides first.
Small intestinal bacterial overgrowth. Breath-test cut-offs, hydrogen vs methane (IMO), root causes, rifaximin and herbal options, and relapse prevention.
Read the guide Pillar guideColonisation vs overgrowth vs invasive infection, what testing can and can’t show, antifungals, biofilms and the die-off myth.
Read the guideThese conditions can produce “IBS-type” symptoms and are not part of the standard IBS work-up. Dedicated guides are in progress; for now, each is summarised so you know what to raise with a clinician.
| Condition | Hallmark clues | How it’s investigated |
|---|---|---|
| Low stomach acid (hypochlorhydria) | Fullness after small meals, reflux that worsens on acid suppression, undigested food, iron or B12 deficiency | Clinical assessment; review of long-term PPI use; specialist testing rarely |
| Bile acid malabsorption | Urgent, watery diarrhoea, often after gallbladder removal or in “IBS-D” | SeHCAT scan or a trial of a bile-acid sequestrant |
| Exocrine pancreatic insufficiency | Pale, greasy, floating stools, weight loss, fat malabsorption | Faecal elastase test |
| Intestinal permeability (“leaky gut”) | Food reactivity, systemic symptoms; a mechanism more than a standalone diagnosis | No validated routine clinical test; addressed by treating the cause |
| Gastroparesis & dysmotility | Early fullness, nausea, bloating worse late in the day | Gastric emptying study; specialist referral |
| Histamine intolerance | Flushing, headaches, reactions to aged/fermented foods and wine | Largely a supervised dietary trial; testing is unreliable |
| Gut-brain axis dysfunction | Symptoms strongly tied to stress; visceral hypersensitivity | Clinical; gut-directed therapies (e.g. hypnotherapy) have evidence |
| SIFO (fungal overgrowth) | SIBO-like symptoms not responding to antibacterial treatment | Small-bowel aspirate (see the candida guide) |
One symptom set, many possible causes. Bloating, pain and altered bowels are the final common pathway of very different problems. That is exactly why a single label rarely settles the question - and why matching the test to the clue matters more than testing everything.
Not sure where you sit? Start with Is it IBS or SIBO? or see which test finds which cause.
Want help working out which of these to investigate first?
Enquire about a consultation