Urine is a potential source of volatile organic compound (VOC) biomarkers, as canines have shown the ability to detect diseases simply by smelling urine headspace. This has prompted researchers to identify VOC biosignatures correlating to many medical conditions, including but not limited to cancer, viral pathogens, and bacterial infections. However, there are an array of variables that may lead to large degrees of urinary VOC heterogeneity in samples, thus making it difficult to identify unique biomarkers and translate the potential of VOCs to clinical applications. To identify significant confounders of VOC expression, urine samples were collected from a large sample cohort of relatively healthy subjects. Blood specimens were also collected for testing comprehensive metabolic panels (CMPs) and complete blood counts (CBCs) to identify any deviations in general health. Urine samples were saturated with salt to increase ionic activity and drive VOCs into the headspace for preconcentration using a solid phase microextraction (SPME) fiber. After sampling through SPME, urinary VOC profiles were quantitatively analyzed by gas chromatography-mass spectrometry (GC-MS) quadrupole time-of-flight (QTOF). Different techniques, including but not limited to relative abundance and autoscaling, were utilized to normalize the integrated signals of the chromatographic peaks corresponding to individual analytes. VOC signals were subject to univariate and multivariate chemometric analyses to identify significant correlations with confounding variables including biological sex, subject age, body mass index (BMI), diet, and even different medications. Similar methods were also implemented to correlate urinary VOC levels to the results of the blood tests (CMP and CBC). Lastly, VOC reproducibility among all subjects was determined by calculating relative standard deviations and 95% confidence intervals. Overall, the results of this study will aid in the understanding of what specific factors significantly effect the concentration levels of VOCs in urine and what should be considered normal interpatient variability. This will help in the future when translating the potential of urinary VOCs for different biomedical applications including noninvasive health monitoring.

Exploring the impact of confounding factors on urinary volatile organic compound biomarker expression by solid phase microextraction and gas chromatography-mass spectrometry

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