SFTPD and acute respiratory distress syndrome: Calfee et al. recently compared biomarker levels in patients with direct versus indirect ARDS enrolled in a single center study of 100 patients and in a secondary analysis of 853 ARDS patients drawn from a multicenter randomized controlled trial [7]: levels of biomarkers of lung epithelial injury (sRAGE, surfactant protein-D) were significantly higher in direct ARDS compared to indirect ARDS.