ANALYSIS AND INTERPRETATION – SEATTLE, WA
ANALYSIS OF SIBO TEST SAMPLES
We’ve partnered with Quintron Instrument Company, a proven leader in the breath testing field for over 40 years, and utilize Quintron’s instrumentation and breath test kits for patient breath collection and analysis. Quintron’s instrumentation is both FDA-registered and ISO-certified, conforming to the latest international quality process standards for medical devices.
Patient breath samples are collected at-home after preparing for the breath test, which includes discontinuation or avoidance of medications or supplements known to influence the breath test and after completing the restrictive diet as outlined in the SIBO test kit instructions. One baseline breath sample is collected prior to substrate consumption (lactulose or glucose), and nine breath samples are collected serially, at 20 minute intervals, over a three-hour period after substrate consumption.
Patient breath samples are returned to the laboratory via USPS, processed for analysis upon arrival, and analyzed on the same day they arrive at our laboratory, which is typically within 4 hours of arrival. According to Quintron, breath samples remain stable for at least 14 days after patient collection.
Patient breath samples are analyzed by gas chromatography using Quintron’s BreathTracker SC Analyzer, which quantifies the concentration of hydrogen, methane, and carbon dioxide in each sample. Carbon dioxide, which is present at relatively low levels in atmospheric air, but at higher concentration in alveolar air, is used as an internal standard to assess the quality of the breath sample and to ensure that the amount of patient breath collected is sufficient for an accurate determination of the hydrogen and methane concentrations in the sample.
Carbon dioxide is also used to normalize each breath sample so that the hydrogen and methane measured in one sample can be accurately compared to the other samples. After normalization, the gases, hydrogen and methane, are reported from each sample in parts per million (ppm). Quintron reports the sampling error of the instrument is +/- 3 ppm for hydrogen and methane and +/-1% for carbon dioxide and the instrument’s linear range to be 0-75 ppm for methane, 0-150 ppm for hydrogen, and 0.1-7% for carbon dioxide.
ANALYSIS AND INTERPRETATION OF SIBO TEST RESULTS
The parameters of our analysis generally conform to the criteria defined by the North American Consensus for Hydrogen and Methane-Based Breath Testing. Specifically, a positive SIBO test is the result of either:
- a rise in hydrogen of 20 ppm or more within the first 100 minutes after substrate consumption, or
- a rise in methane of 10 ppm or more within the first 100 minutes after substrate consumption
Sample quality is determined by carbon dioxide concentration in the breath sample, where carbon dioxide concentrations ≥ 1.4% indicates an amount of patient breath was captured that is sufficient to accurately quantify the hydrogen and methane concentration in the sample. Samples with carbon dioxide concentrations <1.4% are considered invalid samples as the patient breath collection was insufficient or incomplete. Invalid samples are omitted from sample analysis.
In general, an invalid sample(s) does not necessarily invalidate the entire breath test. Usually, if only one or two samples are invalid, the remaining data is often sufficient to accurately determine whether the presence of SIBO exists or not. However, too many invalid samples may make the interpretation of the breath test impossible, and if this occurs, the entire breath test is reported as invalid, and it is recommended that the patient retest.
Far and away, the most common cause of an invalid sample is improper breath collection technique, typically such as:
- inserting the sample collection tube before exhalation begins
- inserting the sample collection tube simultaneously as exhalation begins
- incompletely inserting the collection tube so that the septum of the collection tube is not punctured by the needle of the breath collector
- puncturing the collection tube more than once
Patients should be referred to the breath test instructions found here for proper breath collection technique and should be advised to call us to review the breath collection procedure before attempting to retest.
In rare instances, sample collection tubes that are returned without carefully packaging them for shipment may arrive broken, which also results in an invalid sample that must be excluded from the analysis.
SO-CALLED DOUBLE PEAK
It is generally accepted that the average orocecal transit time for healthy individuals is 90 min +/- 10 min. Also, in healthy individuals, 120 minutes post substrate consumption represents the point at which substrate passes from the small intestine through the ileocecal valve to the colon. In breath tests, this transition is sometimes observed as an inflection point that separates peak gas values observed in the small intestine and in the colon (a so-called double peak plot). However, the presence of SIBO is not always associated with a bimodal curve shape. The absence of a double peak is not always consistent with the absence of SIBO.
HIGH BASELINE GAS VALUES
The baseline gas value measured reflects gases detected in expired breath before the test substrate is consumed and may reflect gases from the following sources:
- incompletely digested food present in the small intestine which is undergoing active fermentation by small intestinal bacteria and/or archaea
- incompletely digested food present in the colon which is undergoing active fermentation by colonic bacteria and/or archaea
- bacterial fermentation occurring the oral cavity
It is, therefore, important that the patient adequately follows the restrictive diet in preparation for the breath test. The restrictive diet consists only of lean proteins and high-glycemic index carbohydrates. Protein fermentation by gut microbes does not produce hydrogen or methane, whereas high glycemic index carbohydrates (e.g., white rice or white bread) are rapidly absorbed and, as such, are not available for significant fermentation by gut microbes. Thus, the restrictive diet serves to limit the non-substrate production of hydrogen and methane that occurs during the breath test. Moreover, patients are advised to thoroughly brush teeth before performing the breath test to remove bacteria from the mouth. Patients should rinse their mouths thoroughly after tooth brushing.
We advise that the restrictive diet be followed for 18-24 hours if the patient is not experiencing constipation or has been diagnosed with slow transit. However, patients with reduced motility as evidenced by constipation or slow transit are advised to follow the restrictive diet for an additional 24 hours (i.e., 42-48 hours) to allow additional time for undigested food to clear the gut. We observe that this additional time significantly improves the ability to resolve a rise in methane gas values during the test.
When baseline values are elevated, the dynamic range of the breath test is reduced, which can result in a falsely low observed rise in gas values, and thus increases the potential for a false negative test result. Typically, high baseline gas values are the result of improper diet preparation prior to testing. If this is observed, the provider should inquire about the patient’s diet preparation and may opt to have the patient retest if it is determined the restrictive diet was not sufficiently followed.