Synonyms Breath Analysis; Breath Test; Hydrogen Breath Test; Hydrogen Exhalation Test

Applies to Bacterial Overgrowth Testing; Carbohydrate Malabsorption Tests; Measurement of Intestinal Transit Time

Replaces Carbon-14 Glycine Cholate Test for Bacterial Overgrowth; Carbon-14 Lactose Breath Test; Carbon-14 Stool Excretion; Intestinal Biopsy (for Disaccharidase Deficiency); Intestinal Intubation for Culture; Intestinal Perfusion and Lactose Barium Radiography; Lactose (Sucrose and d-Xylose) Tolerance Test; Stool pH Test; Tests for Fecal Reducing Substances

Procedure Commonly Includes Carbohydrate intolerance: The patient ingests lactose or other carbohydrate feeding. This is followed by collection of samples of expired air. The H₂ content of the expired air is then determined by gas chromatography. Above average H₂ content is considered a positive test.

Measurement of intestinal transit time: The patient ingests a carbohydrate feeding which is followed by a collection of a series of samples of expired air. The H₂ content of each air sample is determined by gas chromatography. The time period between the ingestion of the carbohydrate meal and the first measured increase in expired H₂ is considered to be the small intestinal transit time.

Bacterial overgrowth: The patient ingests a carbohydrate feeding which is followed by a collection of a series of samples of expired air. The H₂ content of each air sample is determined by gas chromatography. The test is considered positive if two distinct H₂ peaks are detected. The first peak corresponds to carbohydrate fermentation by bacteria in the small bowel, and the second to fermentation in the colon (an abnormal finding). Fasting breath H₂ is also usually elevated in this condition.

Indications Diagnosis of carbohydrate malabsorption - lactose, sucrose, DW xylose;¹ diagnosis of bacterial overgrowth - H₂ breath test is useful in conjunction with carbon-14 glycolate test; diagnosis of motility disorders such as irritable bowel and postgastrectomy syndromes by measurement of intestinal transit time.

Contraindications Patient cannot drink liquids, active diarrhea may decrease response, severe pulmonary disease

Patient Preparation NPO for at least 6-8 hours (preferably overnight) and during test (except for carbohydrate feeding). No smoking 15 minutes prior to test. No antibiotics 7 days prior to test. No grain cereals or foods 12 hours prior to test. Carbohydrate feeding: infants 2 g/kg low fiber, adults 20 g/kg low fiber. Lactulose is best feeding for bacterial overgrowth testing as it traverses the entire bowel unabsorbed.

Specimen Expired air

Container Haldane-Priestly tube for adults; for infants, Rahn-Otis end tidal sampler, nasal prongs, or postnasal catheter connected to bags fitted with 1-way stopcocks. Gas is then transported via an oiled syringe to a Vacutainer®.

Sampling Time Up to 6 hours if interval sampling is used. Interval sampling is usually done every 30 minutes for 2-4 hours.

Collection Usually involves Haldane-Priestly tube into which the patient exhales with nose clamped

Storage Instructions Vacutainer® for up to 3 weeks

Turnaround Time 3-7 days

Normal Findings For lactose intolerance: if measured in rate of excretion, H₂ >0.5 mL/minute (nL <0.3); if measured as end tidal volume, H₂ >24 ppm or 20 ppm greater than fasting (nL <10). For intestinal overgrowth: two distinct H₂ peaks correspond to carbohydrate fermentation in the small bowel and then the colon.¹ For measurement of intestinal transit time: more than 95 minutes is normal.

Limitations If the test is performed during states of active diarrhea, transit time may not be long enough for sufficient fermentation. Significant bowel, pulmonary, or vascular disease may decrease H₂ absorption and secretion. Idiopathic or iatrogenic absence of intestinal flora makes the test worthless. Presence of normal flora that consume H₂ can give falsely low H₂ excretion. The test is useless in newborns prior to intestinal colonization.² The presence of acidic colonic milieu common in infants can give a falsely low H₂ excretion.³ Exercise also lowers H₂ excretion.⁴ Smoking and sleep may falsely elevate H₂ excretion.⁵

Additional Information This test is based on the premise that the normal small bowel absorbs ingested carbohydrate, that the normal small bowel is sterile, and that undigested carbohydrate is then fermented by normal colonic flora with H₂ being the product of that fermentation. The predominence of H₂ produced in the colon is expelled rectally and the remainder is absorbed into the colonic circulation. It is then expelled into the pulmonary tree where it can be measured as exhaled H₂.

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