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FAQ: How useful are breath tests for IBS?

There is some recent interest in breath tests to evaluate IBS. These are breath hydrogen tests after a meal of fructose, lactose and lactulose. Each sugar needs to be tested separately and the test takes 2-3 hours for each sugar. Often just the fructose test is performed. The concept is that response to a FODMAP diet can be predicted by a positive fructose breath test - i.e showing failure of normal absoprtion of fructose (malabsorption). In practice a positive test is very common and has minimal predictive value.

Positive breath tests for lactose may be found in 10-15% of people with IBS and 5% of the general population. Knowledge of a positive test can be helpful although a trial of diary exclusion for a month is perhaps more informative as symptoms from diary products may be due to factors other than the lactose.

Some groups have proposed that bacterial overgrowth in the small bowel causes many of the symptoms of IBS particularly bloating. Tests for this possible abnormality are difficult. A simple test is the lactulose breath test but this is difficult to interpret. There is a relatively high rate of positive tests making it difficult to know if this is a genuine finding. There is an antibiotic called rifaxamin that is claimed to treat this problem. This antibiotic is expensive and has limited availability and is not used in NZ for IBS. There may be some people who will benefit from this treatment if cheaper alternatives are available. it is not clear if repeated courses - perhaps every 3 months - will continue to maintain the improvement in symptoms.

Some tests also check for methane as well as H2 (hydrogen). About 40% of people are methane producers and this will give some extra information. Methane actually slows down the bowel - ? cause or effect. There is debate as to what to do with a positive test (as applies for hydrogen tests)

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