Measuring and reporting the concentration of acetaldehyde in human breath

Most of the acetaldehyde generated during the metabolism of ethanol becomes tightly bound to endogenous molecules such as haemoglobin, amino acids and certain phospholipids. Free acetaldehyde passes the blood-brain barrier and traces of this toxic metabolite are excreted through the lungs and can be detected in the expired air. The blood/air partition coefficient of acetaldehyde at 34 degrees C, the average temperature of end-expired air, is about 190:1. Because of various problems associated with measuring acetaldehyde in blood samples, several research groups have instead investigated the analysis of acetaldehyde in breath which offers an indirect and alternative approach for clinical and research purposes. However, care is needed when interpreting the results of breath acetaldehyde measurements, because of the possibility of local formation from microflora inhabiting the upper airways and mouth. The concentration of acetaldehyde exhaled in breath after drinking alcohol demonstrates large inter-individual differences depending on various genetic (racial) and environmental factors. Moreover, acetaldehyde is an endogenous metabolite and even without drinking any alcohol the concentrations expelled in breath span from 0.2 to 0.6 nmol/l, with higher levels observed in smokers and abstinent alcoholics. Breath acetaldehyde concentration reached between 5 and 50 nmol/l in European subjects who drank a moderate dose of ethanol (0.4-0.8 g/kg), with the highest values seen in smokers. The concentration of breath acetaldehyde in Japanese subjects after drinking alcohol reached between 200 and 500 nmol/l at the peak. These much higher levels follow because a large proportion of Orientals (40-50%) inherit an inactive form of the low Km mitochondrial isoenzyme of aldehyde dehydrogenase (ALDH2). The highest concentration of breath acetaldehyde were seen in healthy Caucasians who drank a small dose of alcohol (0.25 g/kg) after taking the alcohol-sensitizing drug calcium carbimide, which blocks the action of ALDH isozymes. During the most intense acetaldehyde-flush reaction, breath acetaldehyde reached between 200 and 1300 nmol/l, but even these abnormally high concentrations did not interfere with the analysis of ethanol in breath by means of non-specific infrared analysers currently used in many countries for testing drinking drivers.