A breath capture device for determining the concentration of acetone in a breath sample from a user. In some embodiments, the device includes a controller programmed to use stored data to control flow of a breath sample into an analysis chamber as the user exhales into a port. In other embodiments, the device includes a switch responsive to an action by the user that is operable between a first orientation in which breath entering the port preferentially travels through a second flow path and a second orientation in which breath entering the port preferentially travels through a first flow path. In still other embodiments, the device includes a flow regulator both responsive to user action and operable from a first position in which breath entering a port preferentially travels through a second flow path to a second position in which breath entering the port preferentially travels through a first flow path.
