###### Abstract  
Increasing interest is noticed in the potential of volatile organic compound (VOC) analysis as non-invasive diagnostic biomarker in clinical medical practice. The spectrum of VOCs, originating from (patho)physiological metabolic processes in the human body and detectable in bodily excrements, such as exhaled breath, urine and feces, harbors a magnificent source of information. Thus far, the majority of studies have focused on VOC analysis in exhaled breath, aiming at identification of disease-specific VOC profiles. Recently, an increasing number of studies have evaluated the usability of VOC present in the headspace of feces in the diagnostic work-up of a wide range of gastrointestinal diseases. Promising results have been demonstrated particularly in those diseases in which microbiota alterations are considered to play a significant etiological role, such as colorectal carcinoma, inflammatory bowel disease, irritable bowel syndrome, celiac disease and infectious bowel diseases. In addition, fecal VOC analysis seems to have potential as a diagnostic biomarker for extra-intestinal diseases, including bronchopulmonary dysplasia and sepsis. Different methods for VOC analysis have been used in medical studies, such as gas-chromatography mass spectrometry, selected-ion flow tube-mass spectrometry, ion-mobility spectrometry, and electronic nose devices. In this review, the available literature on the potential of fecal VOCs as diagnostic biomarker, including an overview of relevant VOC detection techniques, is discussed. In addition, future hurdles, which need to be taken prior to implementation of VOC analysis in daily clinical practice, are outlined. volatile organic compounds; disease biomarkers; electronic nose; VOC; feces 2018 129 12018 129 12018 129 12018 129 12018 129 12018 129 12018 129 12018 129 12018 129 12018 1201  
disease-specific biomarkers, such as Fecal immunochemical test for hemoglobin (FIT) [1; 2], DNA [3] and microRNA [4] for early detection of colorectal cancer (CRC). Furthermore, inflammation related proteins, such as beta-glucuronidase, have been studied as a potential biomarker in inflammatory bowel disease [5]. These potential biomarkers show great potential, especially fecal DNA and microRNA hold potential in facilitating more individualized treatment approaches. However, a major concern of these biomarkers is the lack of specificity, therefore preventing their application in clinical diagnostic work-up [3; 6]. In the past decades, an increasing number of studies have assessed the usability of volatile organic compound (VOC) analysis as a non-invasive, high-throughput and low-cost diagnostic biomarker VOCs are carbon-based chemicals which under normal indoor atmospheric conditions of temperature and pressure evaporate to the ambient air. They are emitted from the body as a product of both physiological and pathophysiological metabolic processes, and can be detected in sweat, urine, exhaled breath, feces, blood and vaginal secretions [7]. In addition, the intestinal microbiota excrete volatile metabolites which contribute to the (fecal) VOC composition, and microbial changes are therefore considered to be reflected by VOC alterations [8]. Consequently, VOC analysis hypothetically harbors an extensive source of information to be used in the diagnostic work-up of a wide range of diseases. In numerous proof-of-principle studies, VOC profiles have been shown to differentiate healthy state from a variety of diseases, including metabolic, infectious, inflammatory, endocrine diseases and malignancies [9]. Sample acquisition for VOC analysis is relatively easy and, in most cases, non-invasive. In many studies, different considerations are made for the choice of analytic excrete (e.g., urine, feces, and exhaled air), which is mainly based on the disease of interest and readiness of patients to collect certain bodily excrements. Initially, many studies preferred usage of exhaled breath, since it is relatively easy to collect and little patient resistance is experienced.