KL‐6 levels are elevated in plasma from patients with acute respiratory distress syndrome

The acute respiratory distress syndrome (ARDS) is an extreme form of lung injury characterised by disruption to the alveolar epithelium. KL‐6 is a mucin-like glycoprotein expressed on type II pneumocytes. Circulating levels of KL‐6 have diagnostic and prognostic significance in a number of interstitial lung diseases, and when elevated are thought to indicate disruption of the alveolar epithelial lining. In this study, the authors sought to determine whether plasma KL‐6 levels were elevated in patients with ARDS and whether these were associated with aetiology, disease severity, outcome or ventilatory strategy. Plasma samples were collected from 28 patients with ARDS, nine ventilated controls of matched illness severity and 10 healthy individuals. KL‐6 concentrations were measured by enzyme-linked immunosorbent assay. Patients with ARDS had higher plasma levels of KL‐6 (median 537 U·mL−1, interquartile range (IQR) 383–1,119), as compared to ventilated controls (median 255 U·mL−1, IQR 83–338) and normal individuals (median 215 U·mL−1, IQR 149–307). In patients with ARDS, plasma KL-6 levels were higher in nonsurvivors than survivors, and correlated positively with oxygenation index and negatively with arterial oxygen tension:inspiratory oxygen fraction ratio. There were also significant positive correlations with mean and peak airway pressures. Elevated levels of plasma KL‐6 may provide a useful marker for acute respiratory distress syndrome in ventilated patients and have possible prognostic significance. Alveolar epithelial cell damage may be influenced by the nature of mechanical ventilatory support.