In particular, low concentrations of BAL fluid interleukin (IL)-1β appeared to be able to rule out VAP effectively.6 IL-8 and the neutrophil proteases matrix metalloproteinase-8 (MMP-8), MMP-9 and human neutrophil elastase (HNE) also showed promise in excluding VAP.7 We, therefore, conducted a pragmatic multicentre validation study of these five BAL fluid biomarkers in patients with suspected VAP. This evidence concerns the gene MMP9 and ventilator-associated pneumonia.