LAUSR

Background: Particles in Exhaled Air (PExA) allows sampling of protein particles from the peripheral airways. The interindividual variation of PEx (PExA material) seems to be large, but little is known about the intraindividual variation. We sought to evaluate the intra and inter-individual variation of two candidate small airways dysfunction biomarkers: Surfactant protein A (SPA) and Albumin. Methods: 18 patients (8 male/10 female) [13 patients with stable asthma (GINA III-IV) and 5 healthy controls; mean age: 50] were recruited from Glenfield Hospital, UK, and performed 2 PExA sessions on visit 1 and one at 2 weeks and 3 months. All individuals followed repeated airway closure manoeuvres post bronchodilator, and 50-100ng of PEx was collected. Additionally, 9/13 asthmatic patients had a pre-bronchodilator session. Proteins were analysed using ELISA. Results: All samples were above the lower limit of quantification. Inter-individual variation of particles, %SPA and albumin was high (figure 1 A). However, good protein agreement was found within individual, with no evident systematic bias across different sampling sessions (see figure). Conclusions: We demonstrate that %SPA and %albumin from PEx are variable amongst individuals, but stable over three months within an individual, in both health and asthma. Further research is required to determine minimal clinically important differences of PExA biomarkers in asthma.