An apparatus and method for collecting a breath sample are provided. The apparatus has a breath input interface configured to receive exhaled breath, a container connected to the breath input interface for receiving at least some of the exhaled breath, the container having a cavity with a volume that is controllable, and at least one controller configured to control the volume of the cavity to increase at a volume increase rate that is at most equal to a flow rate of the exhaled breath received by the breath input interface.