Abstract: A method to determine a subject's blood glucose level non-invasively by analyzing an exhaled breath or another gaseous emanation from the subject. The method includes non-invasively detecting an amount of at least one volatile organic marker in the subject's exhaled breath or the subject's other gaseous emanation as marker data and determining the subject's blood glucose level based on the marker data. The amount of the volatile organic marker selected is negatively correlated to the blood glucose level.