Apparatus and method for collecting a breath sample using a metering device

An apparatus for collecting a breath sample, comprising:

• a breath input interface configured to receive exhaled breath;
• a metering device configured to determine a constituent level in the breath being received;
• a first conduit system extending from the breath input interface and connected to at least one breath sample storage device;
• a valve positioned along the first conduit system to control a flow of the exhaled breath towards the at least one breath sample storage device;
• and
• at least one controller configured to determine if the constituent level is within a constituent level target range, determine if a change rate in the constituent level is within a constituent level change rate target range, and control the valve to open at least partially based on whether the constituent level is within the constituent level target range and the change rate is within the constituent level change rate target range.