2-AA detection in breath. The peak integration values for 2-AA were significantly higher in CF patients colonised with Ps. aeruginosa than in CF patients not colonised (p < 0.001) with Ps. aeruginosa and healthy subjects (p < 0.0002). The numbers of subjects with detectable 2-AA in each group are shown. The lower limit of detection (peak integration of 88) is shown as a dotted line.