Examination of less common body fluids: part 1 -⁠ pleural fluid.

Overview

This communication provides an overview of the pathophysiology and clinical biochemistry of diseases accompanied by pleural effusions.\\r\\nPathophysiology: Pleural fluid allows a mechanical connection between the lung and the chest wall and facilitates their movement. Its equilibrium is maintained by production and reabsorption, mainly by the lymphatic capillaries. Disturbance of this balance leads to pleural effusion, which can have various causes and forms.
Types of effusions: Pleural effusions are divided into transudates and exudates. Transudates are caused by a disturbance of hydrostatic or oncotic pressure. Exudates are related to increased mesothelial permeability, inflammation or malignancy. Light's criteria facilitate differentiation.
Clinical conditions with pleural effusions: Heart failure is the main cause of transudates, while pneumonia, pericarditis and malignancy lead to exudates. Effusions in tuberculosis, cirrhosis and nephrotic syndrome have specific characteristics according to the etiology.
Laboratory tests: Currently, the abbreviated Light´s criteria are used, i.e. the ratio of protein and LDH in the effusion and serum. In some clinical situations (heart failure with diuretic therapy), an albumin gradient (the difference between serum and pleural fluid albumin concentrations) is preferable. The main components investigated (besides LDH, protein and albumin in the effusion and serum) in pleural fluid include triaglycerides, cholesterol, glucose, natriuretic peptides, pH, some tumor markers. Hematological, cytological, and microbiological tests are also applied.

Conclusion: Examination of pleural effusion is still a necessary part of differential diagnostic evaluation in many clinical situations.

Keywords:

pleural fluid – Light´s criteria – albumin gradient