Diagnosing gastrointestinal illnesses using fecal headspace volatile organic compounds

Abstract

Volatile organic compounds (VOCs) emitted from stool are the components of the smell of stool representing the end products of microbial activity and metabolism that can be used to diagnose disease. Despite the abundance of hydrogen, carbon dioxide, and methane that have already been identified in human flatus, the small portion of trace gases making up the VOCs emitted from stool include organic acids, alcohols, esters, heterocyclic compounds, aldehydes, ketones, and alkanes, among others. These are the gases that vary among individuals in sickness and in health, in dietary changes, and in gut microbial activity. Electronic nose devices are analytical and pattern recognition platforms that can utilize mass spectrometry or electrochemical sensors to detect these VOCs in gas samples. When paired with machine-learning and pattern recognition algorithms, this can identify patterns of VOCs, and thus patterns of smell, that can be used to identify disease states. In this review, we provide a clinical background of VOC identification, electronic nose development, and review gastroenterology applications toward diagnosing disease by the volatile headspace analysis of stool.

Keywords: Electronic nose; Feces; Mass spectrometry; Odors; Volatile organic compounds.

Figure 1

Quadrupole mass filter schematic: ionized gas enters the quadrupole through a slit and interacts with charged metal poles. Based on mass and charge, different ionized gases successfully pass through a second slit to a detector that measures the mass-to-charge ratio of the ionized gas (solid arrow), while other ionized gases will collide with metal rods and will not reach the detector (dotted line and asterisk).

Figure 2

Example output of the owlstone lonestar field-asymmetric ion mobility spectrometry device of breath volatile spectra of limonene (A) and isoprene (B)-volatile organic compounds associated with lung cancer detection. Courtesy of Owlstone Nanotech, used with permission.

Figure 3

Example output of the eNose company aeonose device identifying aggregate volatile organic compounds signal output from clinical breath analysis using its 3-sensor array spanning a 10-min breath sample.