Comparing the Diagnostic Sensitivity and Specificity of Pleural Fluid N-Terminal Pro B-type Natriuretic Peptide (NT-proBNP) and Other Biochemical Gradient Criteria in Distinguishing Heart Failure and Non-heart Failure Related Pleural Effusions (CENTRE Study)

This study is comparing different lab tests — including a marker called NT-proBNP in pleural fluid (fluid from around the lungs) — to better distinguish between fluid buildup caused by heart failure versus other causes. **You may be eligible if...** - You are 18 or older - You have been hospitalized for heart failure and have fluid around your lungs (pleural effusion) - Your doctors have recommended draining and testing the pleural fluid **You may NOT be eligible if...** - You have had previous treatments injected into the same pleural space (such as talc or clot-dissolving drugs) - You have had surgical procedures on the same side of the chest (decortication or pleurodesis) - You had thoracic or cardiac surgery on that side in the past 3 months - You are unable to give informed consent due to refusal or cognitive impairment Talk to your doctor to see if this trial is right for you.