A hydrogen breath test (or HBT) is used as a clinical medical diagnosis for people with irritable bowel syndrome, and common food intolerances. The test is simple, non-invasive, and is performed after a short period of fasting (typically 8–12 hours). Even though the test is normally known as a “Hydrogen Breath Test” some physicians may also test for methane in addition to hydrogen. Many studies have shown that some patients (approximately 35% or more) do not produce hydrogen but actually produce methane. Some patients produce a combination of the two gases. Other patients don’t produce any gas, which are known as “Non-Responders”; it has not been yet determined whether they may actually produce another gas. In addition to hydrogen and methane, some facilities also utilize carbon dioxide (CO2) in the patients’ breath to determine if the breath samples that are being analyzed are not contaminated (either with room air or bronchial dead space air).
Testing may be administered at hospitals, clinics, physician offices or if the physician/laboratory has the proper equipment and breath collection kit, patients can collect samples at home to then be mailed in for analysis.
Many testing kits are emerging in the breath testing market claiming to be able to collect proper samples and providing analytical results to individuals collecting samples at home and sending to laboratories for analysis. Consumers are always urged to call the manufacturers of these test kits and do their research to ensure that the test they are performing is being collected and analyzed properly. There is currently a patented breath-collection test kit offered by a U.S. manufacturer which was designed and patented for the proper collection and storage of breath samples. Proper collection and analysis of samples is imperative in the breath hydrogen testing realm. Some testing kits indicate a patients can blow into a test tube with a straw and close the top in a predetermined amount of time for proper storage and analysis; this method of breath collection for a hydrogen breath test should be confirmed as this means for collection was originally designed to collect a sample from a labels Helicobacter pylori breath test which works well for this method of collection, however other individuals which have performed this method for the hydrogen breath test have had to repeat tests and/or received inconclusive results. This could be due to improper analysis on instrumentation, improper collection from patients, or the test collection method.
Tests vary from country to country, so the following information is provided as a rough guide to typical uses of the hydrogen breath test:
Fructose malabsorption – the patient takes a base reading of hydrogen levels in his/her breath. The patient is then given a small amount of fructose, and then required to take readings every 15, 30 or 60 minutes for two to three hours. The basis of the test is a failure to absorb the given sugar, which is then metabolized by bacteria that give off either hydrogen or methane. Therefore, the more gas that is produced, the less absorption has occurred. If the level of hydrogen rises above 20 ppm (parts per million) over the lowest preceding value within the test period, the patient is typically diagnosed as a fructose malabsorber. If the patient produces methane then the parts per million for the methane typically rises 12 ppm over the lowest preceding value to be considered positive. If the patient produces both hydrogen and methane then the values are typically added together and the mean of the numbers is used to determine positive results, usually 15 ppm over the lowest preceding value.
Lactose malabsorption – the patient takes a base reading of hydrogen levels in his/her breath. The patient is then given a small amount of pure lactose (typically 20 to 25 g), and then required to take readings every 15, 30 or 60 minutes for two to three hours. If the level of hydrogen rises above 20 ppm (parts per million) over the lowest preceding value within the test period, the patient is typically diagnosed as a lactose malabsorber. If the patient produces methane then the parts per million for the methane typically rises 12 ppm over the lowest preceding value to be considered positive. If the patient produces both hydrogen and methane then the values are typically added together and the mean of the numbers is used to determine positive results, usually 15 ppm over the lowest preceding value. However, recent study suggest that testing may not correlate with any actual diagnosis.
Small Bowel Bacterial Overgrowth Syndrome (SBBOS) or Small Intestinal Bacterial Overgrowth (SIBO) – the patient is either given a challenge dose of glucose, also known as dextrose (75-100 grams), or lactulose (10 grams). A baseline breath sample is collected, and then additional samples are collected at 15 minute or 20 minute intervals for 3–5 hours. Positive diagnosis for a lactulose SIBO breath test – typically positive if the patient produces approximately 20 ppm of hydrogen and/or methane within the first two hours (indicates bacteria in the small intestine), followed by a much larger peak (colonic response). This is also known as a biphasic pattern. Lactulose is not absorbed by the digestive system and can help determine distal end bacterial overgrowth, which means the bacteria are lower in the small intestine. Positive diagnosis for a glucose SIBO breath test – glucose is absorbed by the digestive system so studies have shown it to be harder to diagnose distal end bacterial overgrowth since the glucose typically doesn’t reach the colon before being absorbed. An increase of approximately 12 ppm or more in hydrogen and/or methane during the breath test could conclude bacterial overgrowth. Recent study indicates “The role of testing for SIBO in individuals with suspected IBS remains unclear.” 
The excess hydrogen or methane is assumed to be typically caused by an overgrowth of otherwise normal intestinal bacteria.
Other breath tests that can be taken include: Sucrose Intolerance, d-xylose and sorbitol.