Glucose prediction by analysis of exhaled metabolites - a systematic review

Background: In critically ill patients, glucose control with insulin mandates time-and blood-consuming glucose monitoring. Blood glucose level fluctuations are accompanied by metabolomic changes that alter the composition of volatile organic compounds (VOC), which are detectable in exhaled breath. This review systematically summarizes the available data on the ability of changes in VOC composition to predict blood glucose levels and changes in blood glucose levels. Methods: A systematic search was performed in PubMed. Studies were included when an association between blood glucose levels and VOCs in exhaled air was investigated, using a technique that allows for separation, quantification and identification of individual VOCs. Only studies on humans were included. Results: Nine studies were included out of 1041 identified in the search. Authors of seven studies observed a significant correlation between blood glucose levels and selected VOCs in exhaled air. Authors of two studies did not observe a strong correlation. Blood glucose levels were associated with the following VOCs: ketone bodies (e. g., acetone), VOCs produced by gut flora (e. g., ethanol, methanol, and propane), exogenous compounds (e. g., ethyl benzene, o-xylene, and m/p-xylene) and markers of oxidative stress (e. g., methyl nitrate, 2-pentyl nitrate, and CO). Conclusion: There is a relation between blood glucose levels and VOC composition in exhaled air. These results warrant clinical validation of exhaled breath analysis to monitor blood glucose levels.