Abstract: The invention generally relates to systems and methods for determining a concentration of glucose in exhaled breadth. In certain aspects, the invention provides a system including a sample collection module configured to collect a condensate sample produced from a mixture of exhaled breadth from a subject and ambient air. The condensate sample includes exhaled breadth glucose and ambient air glucose. The system also includes an assay module configured to assay the condensate sample for total glucose. The system also includes an analysis module that includes a processor that is configured to determine a total glucose concentration in the condensate sample, and adjust the total glucose concentration based upon a concentration of the ambient air glucose in the condensate sample, thereby determining a concentration of the exhaled breadth glucose in the exhaled breadth from the subject.