Fact: breathalyzers are often inaccurate and commonly unreliable. See "How Breathalyzers Work — and Why They Don't". And one of the many reasons for this inaccuracy/unreliability is that the machines assume the breath sample being measured is alveolar air — that is, air from deep within the lungs. To calculate the amount of alcohol in the blood, the amount of alcohol in the breath sample is multiplied by the breathalyzer's internal computer. If, however, the sample is not from the lungs but from the mouth, throat or stomach, the amount of alcohol should not be multiplied, or the result will be falsely high. But the machine doesn't know any better, so…. (See "The Mouth Alcohol Problem".)
One common source of mouth alcohol is gastroesophogeal reflux disease, known as GERD. How common? According to medical authorities, the lifetime incidence of GERD in the U.S. population is 25-35%. In a person with GERD, alcohol rises from the stomach into the esophogus and oral cavity — to be breathed directly into a breathalyzer. See "High Breathalyzer Readings from Acid Reflux". So you shouldn't take a breath test if you're in that 1/3 of the population.
But you don't have GERD, you say, you're in perfect health — except for this nagging cough…
GERD and Chronic Cough
GERD should be suspected as the cause of chronic cough whenever a patient complains of frequent episodes of typical gastrointestinal symptoms such as daily heartburn and regurgitation, especially when the chest radiograph or clinical picture suggests an aspiration syndrome. Alternatively, cough may be the only symptom of GERD; in prospective studies, such so-called silent GERD has accounted for 43% to 75% of cases. In the absence of gastrointestinal symptoms, chronic cough can be confidently attributed to GERD if the patient is a nonsmoker, is not taking an ACE inhibitor, and has a normal or near-normal chest radiograph, and asthma, upper airway cough syndrome, and nonallergic eosinophilic bronchitis have been ruled out; 92% of patients with silent GERD fit this clinical profile. Failure to obtain a history of nocturnal coughing does not exclude GERD as a cause of cough. When the chest radiograph is normal, cough from GERD most commonly occurs while the patient is awake and upright and it usually does not occur or is not noted at all during sleep. Irwin, "Chronic cough due to gastroesophageal reflux disease: ACCP evidence-based clinical practice guidelines", 129 Chest 129 (1 suppl), 2006.
Chronic cough = GERD = mouth alcohol = false high breath test results.
(Thanks to Troy McKinney of Houston.)