Pleural Effusion Types in Chronic Kidney Disease

The purpose of this observational study is to understand the causes of pleural effusion (a buildup of fluid around the lungs) in patients with advanced Chronic Kidney Disease (CKD Stages 3 to 5). Pleural effusion is a common complication in kidney disease, but it can be caused by many different issues, such as simple fluid overload, heart failure, or infections like tuberculosis. To treat this fluid buildup effectively, doctors need to classify whether the fluid is a transudate (usually caused by pressure imbalances like fluid overload) or an exudate (caused by inflammation, lung disease, or infection). Standard medical formulas, known as Light's Criteria, are typically used to figure this out by comparing proteins in the fluid to proteins in the blood. However, these standard tests may sometimes misclassify the fluid in kidney disease patients because their baseline blood protein and albumin levels are often altered by their condition. Researchers in this study will enroll adult CKD patients (both on dialysis and not yet on dialysis) who have confirmed fluid around their lungs. Participants will undergo a standard, ultrasound-guided procedure called a diagnostic thoracentesis to safely draw a small amount of the chest fluid. At the same time, a routine blood sample will be taken. The study aims to: * Compare the chest fluid to the blood sample using standard criteria, abbreviated criteria, and the Serum-Pleural Effusion Albumin Gradient (SPAG). * Determine the most common underlying causes of lung fluid across different stages of kidney disease. * Identify which diagnostic formula is the most accurate for CKD patients, helping doctors avoid misdiagnosis and provide better, more targeted treatments.