Effectiveness of breath testing correction
Description
Introduction Breath testing of hydrogen (H2) and methane (CH4) is widely used for assessment of carbohydrate malabsorption and small intestinal bacterial overgrowth. Simultaneous breath sampling of oxygen (O2) concentration allows assessment of breath sample quality and potentially adjustment of H2 and CH4 concentration based on this. The following formula has been used for correction commercially and clinically: H2normalised = H2measured x (O2atmospheric – O2reference)/ (O2atmospheric – O2measured) Method 4 volunteers provided sets of 3 breath samples taken very close together: ideal, sub-optimal and deliberately bad. In total 63 pairs of samples presumed to represent the same underlying alveolar breath H2 concentration were collected. The H2 concentration in the worse sample was normalised to the O2 concentration in the better sample using the formula above and compared with the true H2 concentration actually measured in the better sample. Results There was very good correlation between normalised H2 concentration from the worse breath sample and H2 concentration in the better sample for the full range of O2 concentrations measured from 11.4% to 16.0% O2 (R=0.909, P<0.001). The normalised H2 concentration systematically underestimated true H2 concentration by on average 5.6% (paired t-test, t= 5.36, P<0.001). Discussion There is no threshold O2 concentration below which changes in O2 concentration have no effect on measured H2. The normalisation correction algorithm used is effective. For breath testing to be better accepted, widespread agreement on the correction algorithm for O2 concentration and of the reference O2 concentration to correct measured H2 and CH4 concentration is required.
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4 members of staff with experience of breath testing agreed to volunteer for this investigation. Breath sampling was performed using the Bedfont GastroGenius hydrogen/ methane testing system (Bedfont Scientific Ltd, Maidstone, UK), using the option to collect breath samples using breath bags. Testing was performed over a number of days. There was no preparation required for breath sampling. In fact the breath sampling was encouraged to be performed some 2-3 hours after a meal in order for the volunteers to have a raised hydrogen breath level. All 4 volunteers were known from previous testing to have hydrogen gas as their predominant gas output during breath testing. On each occasion 3 separate breath samples were taken as closely together as possible, each performed within a minute of the previous sample. It was therefore hoped that the underlying alveolar hydrogen concentrations would be similar for the 3 breath samples taken. Breath samples were taken in breath sampling bags. The following breath sampling manoeuvres were performed in order to deliberately vary the proportion of alveolar air collected [9]. 1. Attempted ideal breath sample (deep breath, breath hold for at least 15 seconds, steady blowing-out with breath sampling just before end-expiration at the end-point of the expiratory reserve) 2. Intentionally poor breath sample (poor breath intake, little or no breath hold, sampling breath well before the end-point of the expiratory reserve) 3. Medium breath sample (reasonably deep breath, breath hold for ~5 seconds, sampling before the end-point of the expiratory reserve) These were performed in random order in case the breath manoeuvres adversely affected the breath quality of subsequent breath samples. The gas sampling equipment had been calibrated and the calibration checked by a simulated breath sample using a calibrated gas supply before this assessment was performed. The displayed hydrogen concentration, oxygen concentration and correction factor were recorded for each breath sample.
Institutions
- Poole Hospital