Mass spectrometric investigations to obtain the first direct comparisons of endogenous breath and blood volatile organic compound concentrations in healthy volunteers

Volatile organic compounds (VOCs) in breath could be clinically useful for the early detection and diagnosis of diseases, physiological disorders and therapeutic monitoring. However, it is crucial to compare the reliability and precision of breath measurements with those from blood if endogenous VOCs on breath are to be used as biomarkers. Few studies have been undertaken to investigate this, none of which relate to endogenous VOCs in freely breathing subjects. Here we establish the reliability and precision of breath measurements to determine endogenous VOC concentrations in comparison to blood measurements in order to assess the viability of using breath measurements for potential diagnostic and screening purposes. Acetone and isoprene concentration levels in the breath, radial arterial blood and peripheral venous blood and in vivo arterial blood/breath ratios for freely breathing subjects have been determined using mass spectrometric techniques. Mean (range) breath concentrations in parts per billion by volume are 1090 (515–2335) for acetone and 465 (308–702) for isoprene. The mean (range) blood concentrations are: for acetone in radial arterial blood 26 (10–73) μmol/l and in peripheral venous blood 18 (9–39) μmol/l; for isoprene in radial arterial blood 6.8 (3.7–11) μmol/l and in peripheral venous blood 14 (5.5–30) μmol/l. Arterial blood/breath ratios mean (range) are 580 (320–860) for acetone and 0.38 (0.19–0.58) for isoprene. An important finding is that the coefficients of repeatability as a percentage of mean are less than 30% in breath but greater than 70% in blood. This study suggests that breath VOC measurements could provide a more consistent measure for investigating underlying physiological function or pathology than single blood measurements.