Laboratory Diagnostics
SIBO Testing & Diagnosis
How SIBO is diagnosed: glucose and lactulose breath tests, small-intestinal fluid culture, and what blood and stool tests can and cannot tell you.
Breath Testing (Standard of Care)
Measures the hydrogen and methane that gut microbes make from a test sugar (glucose or lactulose). A hydrogen rise of 20 ppm within 90 minutes, or methane of 10 ppm or more, is positive.
Anti-CdtB & Vinculin Biomarkers
Antibodies against a food-poisoning toxin (CdtB) and the gut nerve protein vinculin are markers of post-infectious IBS, not of SIBO itself. Standard blood tests check for B12 and other deficiencies.
Stool Panels & Endoscopy Aspirate
Culture of fluid from the small intestine (more than 1,000 CFU/mL) is the reference test. Stool tests reflect the colon and cannot diagnose SIBO, but can rule out other causes.
Start here
Which test, and when?
Breath tests are the practical first step for most people. The guides below explain what each test can and cannot show.
| Guide | What it shows | Typically used for |
|---|---|---|
| How SIBO is diagnosed | Who should be tested and which test to choose | Start here |
| Breath tests | Glucose detects about 54% of cases with 83% specificity; lactulose about 42% with 71% | Most people |
| Endoscopy & fluid culture | The reference test, but invasive and samples only one spot | Unclear or complicated cases |
| Blood tests | Show deficiencies such as low B12; antibody tests point to post-infectious IBS | Checking for complications |
| Stool tests | Cannot diagnose SIBO; calprotectin and elastase rule out other conditions | Ruling out look-alike conditions |
Diagnostic Guides
Clinical Testing Deep-Dives
