Pleural effusion is a common clinical condition characterized by the accumulation of excess fluid within the pleural space due to disruption of normal pleural fluid dynamics. The etiology is diverse and includes systemic conditions such as congestive heart failure, liver cirrhosis, and renal disease, as well as localized pleural pathologies including infection, malignancy, and inflammatory disorders. Accurate classification of pleural effusion into transudative and exudative types, primarily using biochemical parameters such as Light's criteria, remains the cornerstone of diagnostic evaluation and guides subsequent clinical management.

Recent evidence emphasizes that differentiation based on biochemical and radiological characteristics significantly influences clinical decision-making. Exudative effusions usually reflect pleural inflammation or injury and often require further diagnostic procedures, such as cytological examination or thoracoscopy, to determine specific causes including malignancy or tuberculosis. In contrast, transudative effusions are typically associated with systemic disorders and are generally managed by treating the underlying condition.

Although Light's criteria continue to serve as the standard diagnostic tool, ongoing research seeks to refine diagnostic thresholds and explore adjunctive biochemical markers and imaging modalities to improve sensitivity and specificity in distinguishing effusion types and identifying underlying etiologies.

Several international studies have described the epidemiology and causes of pleural effusion across different populations; however, data from Egypt remain limited, particularly from tertiary care centers such as Mansoura University Hospitals. Understanding the patterns and etiologies of pleural effusion within a specific population-especially in regions with distinct epidemiological characteristics-is essential from both scientific and clinical perspectives.

Accurate categorization into transudative and exudative effusions using biochemical and imaging criteria allows clinicians to tailor the diagnostic approach appropriately. While transudative effusions often require conservative management targeting the primary systemic condition, exudative effusions frequently necessitate more invasive investigations, including pleural biopsy, thoracoscopy, or advanced imaging techniques to establish a definitive diagnosis.

Such stratification helps minimize unnecessary invasive procedures, reduce diagnostic delays, and optimize healthcare resource utilization-particularly in settings with limited access to advanced interventional diagnostics. Furthermore, local data regarding prevalence and clinical presentation provide valuable insights into regional disease burdens, such as higher rates of tuberculosis or malignancy, thereby supporting more effective healthcare planning and targeted management protocols.

Finally, adopting a comprehensive approach that integrates clinical assessment, radiological findings, and pleural fluid analysis aligns with contemporary evidence-based recommendations for pleural disease evaluation, ensuring that the study findings are applicable to both local and international clinical practice.

Inclusion Criteria:

• All patients with documented pleural effusion confirmed by chest imaging (X-ray, ultrasound, or CT).
• Patients with complete clinical, laboratory, and radiological records.

Exclusion Criteria:

• Patients with incomplete medical records.
• Pediatric patients (<18 years).
• Patients with post-surgical pleural collections unrelated to systemic or pathological causes.

Adult patients (>18 years) diagnosed with pleural effusion between January 2020 and December 2025.