My Hydrogen/Methane/H2S Breath Test Was Negative, Can I Still Have Dysbiosis? – Updated 2023


The hydrogen/methane/hydrogen sulfide (H2S) breath test is a diagnostic tool for determining if you are suffering from SIBO or upper gut dysbiosis. Some people still suffer from bloating, excessive gas, reflux, and/or abdominal pain, even though their breath test results are negative.

Is it possible to still have gut dysbiosis if your breath test results were negative?

What is a Breath Test and What are the Positives and Negatives Associated with Breath Tests?

The hydrogen/methane/H2S breath test is a non-invasive fasting test in which your doctor has you breathe into a machine that monitors excess hydrogen, methane, or hydrogen sulfide released by opportunistic bacteria within your digestive tract from fermenting ingested substrates. You are either given glucose or lactulose as a substrate during the test to consume and exhaled test data is collected at twenty-minute intervals for at least three to five hours. Suppose you blow from your breath at least twenty parts per million (ppm) of hydrogen, three ppm of methane, or three ppm of H2S within the first thirty to sixty minutes of the test after the control is measured. In that case, you might be suffering from upper gut dysbiosis. If you blow from your breath at least twenty parts per million (ppm) of hydrogen, three ppm of methane, or three ppm of H2S after the first thirty to sixty minutes and before the final timed test markers, you might be suffering from SIBO (but even a result of twelve ppm hydrogen should be considered at the very minimum). If your hydrogen and methane are flat-lined or do not rise during the test, you may have the third type of SIBO, hydrogen sulfide producing bacterial dysbiosis.

Which substrate is better at determining gut dysbiosis, lactulose or glucose? Lactulose is a synthetic, non-digestible sugar used to treat constipation and reduce the ammonia burden in people with liver disease. Lactulose is a disaccharide formed from one molecule of fructose and galactose. Bacteria must ferment lactulose within our intestinal tract first to absorb any. We lack the necessary enzymes to metabolize lactulose ourselves. Lactulose is only by prescription within the United States. Glucose is a simple sugar (monosaccharide) directly absorbed by our gastrointestinal system and is quickly metabolized by our body. Using glucose as a test marker may give a false negative reading because at least seventeen feet of the small intestine may not be tested. After all, the glucose might be absorbed before it reaches the distal part of the small intestine to see if bacteria ferment it. Furthermore, people dealing with hydrogen-dominant SIBO with diarrhea (fast motility), glucose, or lactulose might reach the cecum (the first part of the large intestine) quicker, creating a false positive SIBO result in people with strictly colonic dysbiosis. If your hydrogen, methane, or H2S levels are normal until the last few timed intervals at the end of the test and you suffer from normal motility or SIBO-D then you might not have SIBO but colonic dysbiosis depending on how elevated your test markers are and if you have abdominal bloating on your sides or below your rib cage.

There are also some issues with the use of lactulose as a substrate. Lactulose decreases bowel transit time as an osmotic laxative, which may also skew the test results. Not all bacteria/archaea strains ferment lactulose, which may cause a false-negative test result. It might be best to perform two tests using both substrates (glucose and lactulose) to accurately determine if you are suffering from dysbiosis. Finally, it may be best to have a bowel transit test done as well, like a sitz marker test to determine one’s motility and how long it will take the substances to reach the large intestine.

The Following are Possible Testing Outcomes:

Your test results show elevated hydrogen (at least twelve ppm) during the beginning of the test. You might be dealing with upper gut dysbiosis of hydrogen-producing bacteria.

Your test results show elevated hydrogen (at least twelve ppm) during the beginning and the middle of the test. You might be dealing with upper gut dysbiosis and SIBO-D from hydrogen-producing bacteria.

Your test results show elevated hydrogen (at least twelve) ppm during the middle of the test. You might be dealing with upper gut dysbiosis and SIBO-D from hydrogen-producing bacteria.

Your test results show elevated hydrogen (above fifty ppm and symptomatic with bloating) at the end of the test. You might be dealing with colonic dysbiosis from hydrogen-producing bacteria.

Your test results show elevated hydrogen (at least twelve ppm) throughout the entire test. You might be dealing with digestive tract dysbiosis from hydrogen-producing bacteria.

Your test results show elevated hydrogen and methane during the beginning of the test, but the gases decrease over time. You might be dealing with upper gut dysbiosis of hydrogen-producing bacteria and methane-producing archaea and possibly SIBO if it maintains elevation during the middle of the test.

Your test results show elevated hydrogen during the beginning of the test. Hydrogen decreases, and methane starts to increase in the middle of the test. You might be dealing with upper gut dysbiosis of hydrogen-producing bacteria and methane-producing archaea dominant SIBO-C.

Your test results show a flat line (all zeroes) of gas production throughout the test. You might be dealing with hydrogen sulfide dysbiosis of the entire digestive tract.

Your test results only show a flat line (all zeroes) of gas production during the middle of the test results. You might be dealing with hydrogen sulfide SIBO.

Your test results only show a flat line (all zeroes) of gas production during the end of the test results. You might be dealing with hydrogen sulfide colonic dysbiosis.

Remember, for most people suffering from archaea dysbiosis; you are probably suffering from hydrogen or hydrogen sulfide producing bacterial dysbiosis as well upstream within your digestive tract because they produce hydrogen that archaea consume, which would decrease the hydrogen/hydrogen sulfide you exhale during a breath test.

The Following is a Link to Recommended Guidelines Before Breath Testing.

People can still have symptoms of SIBO or upper gut dysbiosis, and their breath test results come back negative. How can that be?

There is also no unified medical interpretation of hydrogen/methane/H2S breath tests. Therefore, a doctor might perceive your test results as normal, and they are not. You are suffering from bacterial dysbiosis. If your values are flat lined during a test that does not measure H2S (the Trio-Smart breath test does), you may be suffering from hydrogen sulfide producing bacterial dysbiosis. You might also be suffering from yeast (elevated measured carbon dioxide levels during a breath test might be indicative of yeast dysbiosis) or parasitical dysbiosis that may not be registered during a breath test. I recommend using the hydrogen/methane breath interpretation guidelines by the leading SIBO expert, Dr. Allison Seibecker.

I recommend getting a GI MAP stool test performed by Diagnostic Solutions through your gastroenterologist. I can help interpret the results of your bacterial culture, lactoferrin levels, pH, and antibody levels to determine if you have SIBO. Contact me for health coaching if you are interested.

It is best to tackle your SIBO or upper gut dysbiosis if you are suffering from many of the symptoms, instead of relying on breath test results. If you are not any better within a month of following the FODMAP diet and SIBO/upper gut dysbiosis protocols then bacterial or archaeal dysbiosis was either not your problem in the first place (might be a fungal instead or parasitical), or the protocol was not potent enough to reduce colonies some hardy bacteria including MAP or Klebsiella.

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