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20 ppm or 10 ppm? SIBO Breath Test Interpretation for Patients

· Irina Shtern · MSc Nutrition (Middlesex University) · BANT-registered nutritional therapist · CNHC registered

Patient reviewing breath test report with clinician

Your report most likely shows one of three patterns: an early hydrogen rise suggesting bacterial fermentation higher up the gut, a raised methane level pointing to methanogen overgrowth, or a flat curve that does not meet either threshold. Whatever the shape of your graph, the number alone will not tell you what caused your symptoms. Save the full report, including the graph, and bring it to your clinician along with the symptom diary you kept during testing before anyone decides on treatment.

TL;DR:

  • A positive breath test often reflects timing issues, such as fast or slow transit, which can lead to false positives or negatives.
  • A methane level of 10 ppm or higher indicates methanogen overgrowth, which is more associated with constipation and slower gut transit.
  • The test’s cutoff values and interpretation depend on the substrate used, with lactulose and glucose providing different information about gut fermentation.
  • Proper preparation, including diet and avoiding antibiotics or probiotics before testing, is vital to prevent inaccurate results.
  • Combining graph analysis with symptom diaries and clinical context provides the most accurate diagnosis and guides effective management.
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Table of Contents

How to read the breath test graph and the numbers to watch

A breath test report is really a small table and a line graph, and both matter more than the single word “positive” or “negative” printed at the top. The first thing to find is your baseline, the gas reading taken before you drink the lactulose or glucose solution. Every later number gets compared against the lowest valid baseline, not against zero, because some people start with naturally raised hydrogen or methane.

After the baseline, you will see a series of readings taken at regular intervals, usually every 10 to 30 minutes, for around two to three hours. According to a review of how these tests are interpreted, clinicians read the graph in a set order: substrate first, then baseline, then the rise from that baseline, then specifically what happens in the first 90 minutes, and finally how that timing lines up with any symptoms you recorded.

Commonly used cut-offs include a hydrogen rise of around 20 ppm within 90 minutes, and a methane level of 10 ppm or higher at any point during the test. These figures are widely cited, but individual labs can apply different criteria, so the interpretive key printed on your own report is the one that counts.

A rise that happens late, well after 90 minutes, is usually read as colonic rather than small-bowel fermentation according to standard clinical practice, which is why timing matters as much as the size of the rise itself.

Some reports also include a carbon dioxide reading, used to calculate a correction factor for how well you exhaled into the collection device. A poor correction factor is a practical warning sign.

Hydrogen versus methane: what each gas suggests about symptoms and treatment

Hydrogen and methane are produced by different microbial populations in your gut, and each tends to track with a different symptom pattern. Hydrogen-producing bacteria ferment carbohydrate and are more often associated with diarrhoea, bloating and audible gas. Methane is produced by archaea called methanogens, and higher methane levels are more often linked with constipation and slower transit.

A methane reading of 10 ppm or higher at any point during the test is the threshold most commonly used to flag what is now called intestinal methanogen overgrowth, or IMO, according to the same interpretive review. Hydrogen thresholds vary more between guidelines, which is one reason two labs can classify the same patient differently, a point confirmed by a study comparing consensus parameters.

IMO is conceptually distinct from hydrogen-dominant SIBO rather than a variant of it. Methanogens are archaea, not bacteria, and the overgrowth pattern they create tends to respond differently to dietary and clinical approaches, which is part of why getting the gas type right matters as much as getting a number right.

Pro Tip: Note which symptoms you felt and when during the test itself, not just your usual symptoms: a clinician reading your graph alongside a timed symptom diary gets a far clearer picture than the numbers alone.

Substrate and timing: how lactulose and glucose change the curve

The substrate you drank before testing shapes the whole curve, so a lactulose report and a glucose report need to be read differently. Lactulose is not absorbed by the gut, so it travels the full length of the small bowel and into the colon, which means it can survey a longer stretch of gut and sometimes produces a double peak, one early and one later as the substrate reaches the colon.

Glucose, by contrast, is absorbed early in the small intestine. That makes it more specific to fermentation happening higher up, but it can miss overgrowth sitting further along the bowel, since little substrate is left to reach it. The European guideline on hydrogen breath testing reports glucose sensitivity of around 62% against lactulose sensitivity of around 52%, figures that are protocol and study dependent rather than fixed constants.

Transit speed complicates both substrates. If the substrate moves through your gut faster than average, a lactulose test can show an early rise that looks like small-bowel fermentation but is actually the substrate arriving in the colon sooner than the standard 90-minute window assumes, a known source of false positives. Slow transit creates the opposite problem: a true small-bowel overgrowth can be missed because the substrate has not reached the fermenting bacteria within the fixed cut-off time, producing a false negative. Review material on oro-caecal transit time cites a median around 105 minutes, with a typical range of 90 to 135 minutes, which sits uncomfortably close to the standard cutoff itself.

Your report should state the substrate used and its dose, along with the lab’s own cut-off values, because these details change what a given number actually means.

Common sources of error and limitations that can change interpretation

Breath tests are sensitive to technique, and a surprising number of unusual or borderline results trace back to preparation rather than biology. NHS patient guidance on home lactulose breath testing stresses that not following the preparation instructions closely risks an inaccurate result.

  1. Diet non-compliance in the day before testing, since residual fermentable carbohydrate can raise baseline gas before you even start.
  2. Toothbrush or mouthwash residue, antibiotics, or probiotics taken too close to the test, all of which can alter gut bacteria or baseline readings.
  3. Sampling errors such as talking before exhaling into the bag, not sealing collection bags properly, or submitting samples late, which the UCLH patient information flags as a common practical reason for uninterpretable results.
  4. Physiological factors such as unusually fast or slow transit, a history of bowel surgery, or motility disorders, all of which shift the timing the standard cut-offs assume.
  5. Low hydrogen producers, a recognised minority who produce little hydrogen regardless of bacterial load, which can mask a genuine overgrowth on a hydrogen-only reading.

When a result looks inconsistent with your symptoms, or the preparation was clearly imperfect, a repeat test, a different substrate, or a decision to manage symptoms without further testing are all reasonable next steps depending on the clinical picture.

Pro Tip: If you remember breaking any preparation rule, however minor it felt at the time, mention it to your clinician before they interpret the graph: it can change the reading entirely.

How to use your report in clinic: what to bring and what happens next

Walking into your follow-up appointment with the right paperwork makes the conversation far more useful than the graph on its own. NHS protocols for both hospital-based and home testing recommend bringing the full report with its plotted graph, a list of any medications or supplements you take, a note of your recent bowel habits, and your symptom diary from the test itself, details confirmed in the UCLH testing information.

Clinicians weigh several things together rather than reading the headline result in isolation: whether your symptom pattern leans towards diarrhoea or constipation, which substrate was used and whether the timing fits the standard windows, and whether the sampling itself looks technically sound. A study on consensus guidelines found that combining interpretation criteria with symptom correlation reduces the risk of misclassifying a patient based on the number alone.

What clinicians check Why it matters
Symptom phenotype (diarrhoea vs constipation) Points towards hydrogen or methane-dominant patterns
Substrate and dose used Changes expected sensitivity and timing of the curve
Sampling quality and CO2 correction Flags results that may not be reliable
Transit history and prior surgery Explains early or late rises that do not fit standard cut-offs

Broad management after a positive result typically starts with dietary adjustment, such as the low FODMAP approach for diarrhoea-predominant symptoms, before any further testing or specialist referral is considered. A positive test is a starting point for that conversation, not an endpoint.

How Food Connection supports breath-test interpretation and follow-up care

Some nutrition consulting services offer laboratory test analysis and interpretation alongside personalised nutrition planning, so a breath test report does not have to sit unexplained in an inbox. The usual pathway starts with an initial consultation where your report, including the graph and timing data, is reviewed alongside your symptom history, followed by written personalised recommendations tailored to what the gas pattern and your phenotype suggest.

From there, follow-up consultations track how your symptoms respond to dietary changes, with a programme-based structure offering continuous support rather than a single one-off review. If bloating is your main complaint, a short practical plan like cutting fizzy drinks for a week can sit alongside this kind of interpretation work. Bringing your full report and symptom diary to the first consultation gives the practitioner the clearest possible starting point.

Author perspective: limits of breath testing and why context matters

Breath testing estimates where fermentation is happening by timing, not by looking directly at your gut. That is a useful estimate, not a definitive anatomical test, and treating a single number as a verdict risks missing what actually matters: whether the gas rise lines up with the symptoms you felt during the test. Quality of sampling and careful reading of the whole curve, not just the headline figure, are what separate a useful interpretation from a misleading one.

— Irina

Book a lab-interpretation consultation with Food Connection

If your breath test report has left you with more questions than answers, Food Connection’s lab interpretation service reviews the full graph, timing and gas pattern alongside your symptom history rather than just the headline result. That review can feed into a programme-based follow-up, built around an initial consultation and written personalised recommendations rather than a single rushed appointment.

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Details of consultation packages, including the initial session and follow-up pricing, are listed on the prices page. If you would rather see the full range of services first, including one-to-one nutrition support and lab interpretation, that page sets out what each pathway involves. Bring your report and symptom diary, and get in touch to arrange a consultation.

Sources

For readers who want to go deeper than this guide, the following sources informed the interpretation guidance above and are worth reading directly.

Always check the specific interpretive criteria printed on your own lab’s report, since these can differ from the figures cited above. Readers comparing non-invasive testing options more broadly may also find this guide to digestive intolerance testing useful background.

This article is general information, not a substitute for advice from a qualified doctor. Consult a qualified healthcare professional about your own circumstances before acting on anything here.

FAQ

What’s the worst food for SIBO symptoms?

There is no single worst food, since trigger foods depend on whether your pattern is hydrogen or methane-dominant and what your personal tolerance looks like. Highly fermentable carbohydrates tend to provoke symptoms most often, which is why structured approaches like the low FODMAP diet are commonly used as a starting point.

Will a colonoscopy pick up SIBO?

A colonoscopy examines the colon and lower small bowel for structural problems and is not the standard way to diagnose small intestinal bacterial overgrowth. Breath testing, which measures hydrogen and methane gas over time, is the test typically used instead, as explained in the UCLH patient information.

What is considered a high SIBO breath test result?

A commonly cited threshold is a hydrogen rise of around 20 ppm within the first 90 minutes, or a methane reading of 10 ppm or higher at any point, according to the interpretive review. Labs can apply slightly different cut-offs, so the criteria printed on your own report take priority over any general figure.

Why do some doctors not believe in SIBO testing?

Some clinicians are cautious because different substrates, doses and consensus cut-offs can classify the same patient differently, a problem documented in a study comparing interpretation criteria. That variability means a positive result is not firm proof that SIBO explains a given patient’s symptoms, which is why many clinicians combine the test with symptom correlation and clinical history rather than relying on the number alone.

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Educational overview; not a substitute for medical diagnosis.