When alcoholic drinks are consumed, a small amount of alcohol is excreted from the blood into the breath allowing breath testing devices to be used to measure a person’s alcohol level.
When we exhale, air is expelled first from the mouth, then from the upper airway and finally from deep within the lungs. Approved evidential breath testing devices continuously monitor exhalations and only measure the alcohol level in the breath once deep lung air is reached, This gives the most reliable indication of the alcohol level in the blood.
By continuously monitoring an exhaled sample, breath testing devices can also distinguish alcohol from the mouth cavity (present at a higher concentration) from alcohol within deep lung air. On detecting mouth alcohol, testing devices will abort the procedure and display the error message, ‘mouth alcohol’, on the test printout.
In a similar manner, if alcohol is present in the stomach during an occurrence of acid reflux or a sudden regurgitation of stomach content, this should be detected as ‘mouth alcohol’ by an approved device and will not elevate a breath test result. However, a recent study by Booker and Renfroe in 2015 (J. Forensic Sciences, Vol.60. No.6. pp1516-1522), using 10 subjects with a medical history of gastro oesophageal reflux disease, has found that this understanding of how reflux affects a test result may be flawed.
The study monitored, simultaneously, the rise and fall of blood and breath alcohol levels in the 10 subjects after they had been given recorded doses of alcohol following a meal. Differences were apparent between the subsequent blood and breath alcohol levels in the same subject and the study suggests that gastro oesophageal reflux disease could be a viable explanation for the difference. The authors suggest that, in subjects with the disease, it may be possible for alcohol vapour to pass constantly from the stomach into the oesophagus and this may not be detectable as “mouth alcohol” even by an approved device.
The study found that during the alcohol absorption phase, breath alcohol levels were elevated by up to 14µg%. However, elevation of breath alcohol did not occur once the alcohol had been completely absorbed and had passed out of the stomach into the blood (usually around 2 hours after drinking). For clients with breath test results below 50µg% in England & Wales or below 40µg% in Scotland, gastro oesophageal reflux disease may be a factor to consider in their defence.
Jenny Gray, Keith Borer Consultants