Unique methodological characteristics of the urine in volatile organic compound analysis

Abstract

Abstract We read with interest the review article by Roland Becker [1] . The author compared between urine and breath biological sampling for detection of cancer related volatile organic compounds (VOCs). At present breath sampling has limitations, particularly due to the Coronavirus (COVID-19) pandemic [2] . Adding to this, breath sampling is also limited by the presence of both endogenous and exogenous VOCs in exhaled air [3] . In contrast, urine as a medium for VOCs analysis has strong characteristics that favour its application in future diagnostic longitudinal cancer studies [4] . Urinary VOCs were already able to differentiate between controls, hepatocellular cancer, urinary bladder cancer, prostate cancer and colorectal cancer [5] , [6] . Urine samples have been shown to remain stable for VOC analysis at room temperature for up to 12 hours [7] . In addition, leaving urine samples stored at 4°C for up to 24 hours demonstrated no significant difference in the chemical composition of VOCs [8] . The optimum temperature for storing urine for VOCs analysis was found to be -80 o C, with storage time of up to one year [9] , [10] , [11] . Two studies showed two to nine cycles of -80 o C freezing and thawing revealed stable VOC results [10] , [11] . Another characteristic that distinguish urine as a biological sample in VOCs analysis is the ability to undergo freeze-drying as an alternative to freezing. This was shown to have potential as an alternative method for VOCs analysis [12] . Furthermore, in comparison to breath sampling urine collection from patients may be more acceptable. The emerging literature on urinary VOCs in cancer has an exploratory nature. Therefore, it is paramount for researchers to develop a consensus to standardise the methodologies in urine sampling, VOC analysis and design of robust longitudinal studies. However, the future is bright for application of urine as a biological specimen in cancer VOCs diagnostics for all the aforementioned unique characteristics.