Noninvasive diagnostic tests that analyze exhaled breath after ingestion of a specific substrate (sugar, urea, etc.).

Work on the principle that bacteria or enzymes in the gut break down the substrate, producing gases (hydrogen, methane, carbon dioxide, or labeled carbon).

These gases are absorbed into the bloodstream, carried to the lungs, and exhaled → measured in the breath sample.

Types & Clinical Uses of Breath Tests

Urea Breath Test (UBT)

Substrate: Urea labeled with C¹³ or C¹⁴

Detects Helicobacter pylori infection (causes ulcers, gastritis).

Principle: H. pylori produces urease, breaking down urea → labeled CO₂ detected in breath.

Hydrogen Breath Test (HBT)

Substrates: Lactose, fructose, lactulose, or glucose

Measures hydrogen/methane produced by bacterial fermentation.

Used for:

Lactose intolerance (malabsorption)

Fructose intolerance

Small intestinal bacterial overgrowth (SIBO) (glucose or lactulose breath test).

Methane Breath Test

Often combined with hydrogen measurement.

Useful for detecting methane-producing bacteria in SIBO, sometimes linked to constipation-predominant IBS.

13C-Octanoic Acid Breath Test

Evaluates gastric emptying (delayed emptying = gastroparesis).

Advantages

Noninvasive, safe, outpatient test.

No need for endoscopy or biopsy in many cases.

Limitations

False positives/negatives possible (affected by antibiotics, PPIs, bowel transit time).

Requires proper patient preparation (e.g., fasting, diet restrictions before test).