Three questions — three instruments
Gut diagnostics is not a single test. It is a battery of functional analyses answering specific clinical questions. GI Effects®, the SIBO breath test and Organix® measure fundamentally different things in fundamentally different parts of the gastrointestinal tract — and with fundamentally different methodology.
The clinical error occurs when the patient or clinician assumes that a negative result from one of these tests rules out gut pathology. It does not. It rules out only the specific question that test was designed to answer.
GI Effects® — the complete large intestine profile
GI Effects® Comprehensive Stool Profile from Genova Diagnostics is the most comprehensive stool panel available in clinical practice. The technology combines quantitative PCR (eDNA), MALDI-TOF mass spectrometry, immunochemistry and culture — four analysis methods on one specimen.
The test measures six clinical domains: microbiome composition and functionality (short-chain fatty acids, beta-glucuronidase), digestive capacity (pancreatic elastase, faecal fat), gut inflammation (calprotectin, eosinophil protein X), immunological markers (secretory IgA), barrier integrity (zonulin) and parasitology (including PCR for Giardia and Cryptosporidium).
Indicated when
- IBS-like symptoms (bloating, diarrhoea, constipation, altered bowel habits)
- Suspected dysbiosis without a specified cause
- Autoimmune conditions with intestinal component
- Chronic low-grade inflammation without identified source
- Follow-up of gut health treatment protocols
- Hormonal imbalances (beta-glucuronidase affects oestrogen metabolism)
SIBO breath test — the small intestine's bacterial picture
Small Intestinal Bacterial Overgrowth (SIBO) is a specific clinical entity: bacteria from the large intestine colonise the small intestine, where they compete with the host for nutrients and produce gases (hydrogen and methane) that cause characteristic symptoms.
The SIBO test is a breath test. The patient ingests lactulose — a non-absorbable sugar substrate — and breathes into collection tubes at set intervals over three hours. Hydrogen and methane gas are analysed; an early hydrogen or methane peak confirms small intestinal bacterial overgrowth. Methane-producing SIBO (IMO — intestinal methanogen overgrowth) produces a distinct clinical pattern with predominant constipation.
Indicated when
- Predominant bloating occurring rapidly after meals (small intestine, not large)
- Previous SIBO diagnosis to be confirmed or excluded
- Conditions associated with motility disorders (hypothyroidism, diabetes, scleroderma)
- Recurrent gut symptoms despite elimination protocols
- Malabsorption without explained aetiology
- Patients with constipation-dominant IBS (methane profile)
SIBO and GI Effects reveal different things and are not alternatives to each other — they are complements. A patient can have verified SIBO (positive breath test) and a normal GI Effects profile, and vice versa. In our clinic we frequently see that SIBO-positive patients have reduced secretory IgA and elevated calprotectin in GI Effects — a pattern suggesting that SIBO is driven by impaired immunological defence in the gut rather than motility dysfunction alone.
Organix® — the systemic signature of dysbiosis
Organix® Comprehensive Profile (urinary organic acids) analyses metabolites in urine produced by the metabolism of gut bacteria and fungi. Unlike GI Effects, which identifies organisms in stool, Organix measures what these organisms produce and how their metabolites affect host biochemistry.
The test detects arabinose (Candida marker), D-lactate (sign of bacterial fermentation), hydroxyphenylacetic acid and hydroxyphenyllactic acid (catabolic markers associated with dysbiosis), along with markers for mitochondrial function, B-vitamin status and neurotransmitter metabolism.
The clinically unique aspect of Organix is that it links gut dysbiosis to systemic biochemical consequences. A patient with normal gut flora in stool may have an Organix profile showing that residual metabolites from yeast or bacterial overgrowth are disrupting central metabolic pathways.
Indicated when
- Chronic fatigue and brain fog without clear gut cause in GI Effects
- Suspected Candida overgrowth with systemic impact
- Skin manifestations that may have a dysbiotic gut component
- Psychiatric symptoms (depression, anxiety) with suspected gut-brain axis involvement
- Recurrent yeast infections
- Complementing GI Effects when systemic impact is unclear
Decision matrix — which test, when
| Clinical question | GI Effects® | SIBO test | Organix® |
|---|---|---|---|
| Large intestine microbiome | ✓ Primary | — | — |
| Small intestine bacteria | — | ✓ Primary | Indirect |
| Fungal overgrowth (Candida) | Culture | — | ✓ Primary |
| Gut barrier (zonulin) | ✓ | — | — |
| Gut inflammation | ✓ Calprotectin | — | — |
| Systemic metabolic impact | — | — | ✓ Primary |
| Digestive capacity | ✓ Elastase, fat | — | Indirect |
| Neurotransmitter impact | — | — | ✓ |
Clinical sequencing — when all three are needed
In complex cases involving IBS, chronic fatigue, autoimmunity or psychiatric symptoms, it is rational to order all three tests in parallel. They do not answer overlapping questions — they answer three distinctly different layers of the gut picture.
GCR logic governs the sequence: GI Effects identifies the large intestine's primary constraint and barrier integrity; SIBO reveals whether the small intestine is contributing gas production and malabsorption; Organix shows whether dysbiosis metabolites are reaching systemic biochemical impact. Treatment order follows the hierarchy — not the order in which symptoms are most prominent.
A negative GI Effects result is routinely used to rule out gut problems. It is a logic error. GI Effects rules out large intestine pathology — not small intestinal overgrowth and not systemic dysbiotic metabolic impact.
If you have bloating, altered bowel habits and general digestive discomfort, GI Effects® is the broadest starting tool — it gives a complete picture of what is actually in the gut and how it is functioning.
If your bloating comes quickly after eating, you have more symptoms in the upper abdomen and elimination diets have not helped — the SIBO breath test is more specific. It measures the small intestine, which GI Effects does not primarily address.
If you have symptoms like brain fog, skin problems or fatigue that do not seem connected to an obvious gut cause — Organix® reveals whether gut bacteria and fungi are affecting your metabolism at the systemic level.