A 
system is provided for sensing an 
analyte in a breath sample. The 
system includes a breath bag, a 
cartridge and a base. The breath bag contains the breath sample. The bag includes a 
mouthpiece fixedly disposed on the breath bag. The 
cartridge includes an interactant that reacts with the 
analyte and generates a change in an optical characteristic relative to a reference. The base includes a flow path, a breath bag 
receiver for detachably receiving and retaining the 
mouthpiece of the breath bag in fluid communication with the flow path, and a 
cartridge receiver that detachably receives and retains the cartridge in the base, such that the base engages the cartridge so that the interactant is in fluid communication with the flow path. The base further includes a flow 
handling system in fluid communication with the flow path, an optical subsystem for sensing the change in the optical characteristic, a processor operatively coupled to the flow 
handling system and the optical subsystem, and a 
user interface operatively coupled to the processor and comprising a start command. Upon user selection of the start command, the processor is configured to automatically regulate the flow 
handling system to move the breath sample in the flow path and to contact the breath sample and the interactant. Upon the occurrence of a predetermined process parameter, the processor is configured to automatically regulate the optical subsystem to sense the change in the optical characteristic, to correlate the sensing of the optical 
system with information about the 
analyte in the breath sample, and to output the information about the analyte in the breath sample to the 
user interface. Related methods also are provided.