In some embodiments, a negative pressure wound therapy system can detect and classify one or more operational conditions, including detection of a wound bleeding. The system can react to detection of blood by providing an indication, reducing the intensity or stopping therapy, releasing negative pressure, etc. In certain embodiments, the system can detect one or more additional operational conditions, such as change in vacuum pressure, gas leak rate change, exudate flow rate change, water flow rate change, presence of exudate, presence of water, etc. The system can detect and distinguish between different operational conditions and provide indication or take remedial action.