Sputum procalcitonin: a potential biomarker in stable bronchiectasis

Sputum procalcitonin is elevated in exacerbations of bronchiectasis. The primary aim of this study was to investigate whether sputum procalcitonin levels are higher in patients with stable bronchiectasis than in healthy controls. We also assessed differences in procalcitonin levels in spontaneously expectorated and induced sputum samples and their repeatability 1 week later. Participants included were aged over 18 years and either had radiologically confirmed bronchiectasis or were healthy controls. Patients with bronchiectasis were clinically stable for at least 6 weeks and had spontaneous and induced sputum collected at visit 1 and again 7 days later. Only induced sputum samples were collected from healthy controls during visit 1. Sputum procalcitonin concentrations in sputum were measured. In total, 30 patients with bronchiectasis and 15 healthy controls were enrolled in this observational study. In the pooled data from visit 1 and 2, the geometric mean procalcitonin level in induced sputum was significantly higher in the bronchiectasis group than in the healthy control group (1.5 ng·mL^-1, 95% CI 1.0-2.1 ng·mL^-1 versus 0.4 ng·mL^-1, 95% CI 0.2-0.9 ng·mL^-1; mean ratio 3.6, 95% CI 1.5-8.6; p=0.006). Mean procalcitonin level was higher in spontaneous sputum than in induced sputum at visit 1 (1.8 ng·mL^-1, 95% CI 1.2-2.7 ng·mL^-1 versus 1.1 ng·mL^-1, 95% CI 0.7-1.8 ng·mL^-1) and visit 2 (1.5 ng·mL^-1, 95% CI 1.0-2.5 ng·mL^-1 versus 1.2 ng·mL^-1, 95% CI 0.8-1.6 ng·mL^-1; p=0.001). Repeating spontaneous and induced sputum procalcitonin levels 1 week later produced similar concentrations (p=0.29, intraclass correlation coefficient (ICC)=0.76 and p=0.72, ICC=0.70, respectively). Sputum procalcitonin is increased in patients with stable bronchiectasis and has potential as a biomarker of airway inflammation and infection in bronchiectasis.