Various methods, computing devices, and systems for collecting breath from a subject are described. In one aspect, a method for collecting breath from a subject includes capturing a target sample from an exhaled breath of a subject having a target concentration of a target volatile organic compound (VOC). The target sample of the target VOC is captured from the non-alveolar volume fraction of the exhaled breath, and the exhaled breath represents the lung capacity of the subject. The target concentration of a target VOC can be, for example, an elevated or a lowered concentration of the target sample of exhaled breath relative to the remaining fractions of the exhaled breath, and can found in a particular fraction of the exhaled breath depending on the particular compound targeted for collection or analysis.
