Project Summary/Abstract Acute respiratory distress syndrome (ARDS) accounts for 10% of admissions and 30% of mortality in intensive care units. Despite extensive basic and clinical research, hospital mortality for patients with ARDS remains as high as 45%. Major reasons for the lack of effective therapies include the lack of tools for predicting which patients will develop ARDS and the difficulty of differentiating ARDS from other causes of pulmonary edema like congestive heart failure (CHF). Because of such diagnostic uncertainty, fewer than half of ARDS cases are recognized, and ARDS-specific therapies are underutilized by 25% worldwide. Using plasma samples from the Fluid and Catheter Treatment Trial (a randomized controlled trial of liberal versus conservative fluid management) in patients with ARDS, and the Treatment of Preserved Cardiac Function Heart Failure with an Aldosterone Antagonist trial (a randomized trial of spironolactone in patients with heart failure with preserved ejection fraction), we will in AIM 1 determine how well serum Siglec-9 distinguishes between ARDS and CHF and in AIM 2 Correlate Siglec-9 levels with ARDS severity and clinical outcomes. The results of this work have tremendous potential to enable earlier diagnosis, treatment, and prognostic assessment of patients with ARDS.