Optimized Sampling Conditions for Fecal Volatile Organic Compound Analysis by Means of Field Asymmetric Ion Mobility Spectrometry

Abstract

Fecal volatile organic compounds (VOCs) are increasingly considered to be potential noninvasive, diagnostic biomarkers for various gastrointestinal diseases. Knowledge of the influence of sampling conditions on VOC outcomes is limited. We aimed to evaluate the effects of sampling conditions on fecal VOC profiles and to assess under which conditions an optimal diagnostic accuracy in the discrimination between pediatric inflammatory bowel disease (IBD) and controls could be obtained. Fecal samples from de novo treatment-naïve pediatric IBD patients and healthy controls (HC) were used to assess the effects of sampling conditions compared to the standard operating procedure (reference standard), defined as 500 mg of sample mass diluted with 10 mL tap water, using field asymmetric ion mobility spectrometry (FAIMS). A total of 17 IBD (15 CD (Crohn's disease) and 2 UC (ulcerative colitis)) and 25 HC were included. IBD and HC could be discriminated with high accuracy (accuracy = 0.93, AUC = 0.99, p < 0.0001). A smaller fecal sample mass resulted in a decreased diagnostic accuracy (300 mg accuracy = 0.77, AUC = 0.69, p = 0.02; 100 mg accuracy = 0.70, AUC = 0.74, p = 0.003). A loss of diagnostic accuracy was seen toward increased numbers of thaw–freeze cycles (one cycle, accuracy = 0.61, AUC = 0.80, p = 0.0004; two cycles, accuracy = 0.64, AUC = 0.56, p = 0.753; and three cycles, accuracy = 0.57, AUC = 0.50, p = 0.5101) and when samples were kept at room temperature for 180 min prior to analysis (accuracy = 0.60, AUC = 0.51, p = 0.46). Diagnostic accuracy of VOC profiles was not significantly influenced by storage duration differences of 20 months. The application of a 500 mg sample mass analyzed after one thaw–freeze cycle showed the best discriminative accuracy for the differentiation of IBD and HC. VOC profiles and diagnostic accuracy were significantly affected by sampling conditions, underlining the need for the implementation of standardized protocols in fecal VOC analysis.

Application of Electronic-Nose Technologies and VOC-Biomarkers for the Noninvasive Early Diagnosis of Gastrointestinal Diseases

“…Several key issues need to be addressed before VOC analysis with e-nose instruments can achieve their full potential as disease detection and monitoring tools for clinical diagnoses. New priority research efforts need to be focused on developing universal standardization of e-nose instruments, sampling protocols, sample transport and storage conditions and analytical methodologies to allow inter-study data comparisons [ 123 , 124 ]. Additional work also is required to identify and expand the list of chemical disease biomarkers known for specific diseases and the unique VOC profile signatures that are indicative of unique complex mixtures of specific biomarker metabolites found in clinical samples which are associated with individual diseases.…”

Applications of Electronic-Nose Technologies for Noninvasive Early Detection of Plant, Animal and Human Diseases

“…Important issues need to be addressed before VOC analysis with e-nose instruments can achieve their full potential as effective disease detection and monitoring tools for clinical diagnoses. Additional priority research should focus on developing universal standardization of e-nose instruments, sampling protocols, sample transport and storage conditions and analytical methodologies to allow inter-study data comparisons [237,238]. The future development of specific disease-associated e-nose databases (with worldwide accessibility by healthcare professionals and researchers based on specific standardized diagnostic methods and instrument types) [239], the identification of additional effective VOC-biomarkers of specific diseases for confirming diagnoses, the development of new potential clinical e-nose applications for detecting additional diseases (e.g., epilepsy) [240], and improvements in electronics miniaturization, ergonomics and diagnostic software should permit e-nose instruments and methods to be fully accepted and integrated into clinical procedures.…”

Developing Electronic-nose Technologies for Clinical Practice

“…Specific changes in microbiome bacteria composition in the gut, due to diseases occurring in the GI-tract and other parts of the body, have provided strong indications of particular diseases. These changes may be detected by e-nose analysis of headspace VOCs derived from fecal samples taken from diseased patients [16]. Dysbiosis also may occur in other parts of the body besides the gut, such as in the oral cavity, lower airways, lungs and kidney where microbiota perturbations have been associated with disease states in other organs and compartments of the body [17][18][19][20].…”