transudaatin

Transudation, also known as transudation (transudate), is the movement of fluid from blood vessels into surrounding tissues or cavities through intact endothelium, driven by differences in hydrostatic and oncotic pressures. The resulting transudate is typically a clear, low-protein, low-cell fluid produced by non-inflammatory filtration rather than by tissue injury.

Mechanism and causes. Transudation occurs mainly when the balance of Starling forces shifts toward filtration: increased hydrostatic pressure in the vascular space or decreased plasma oncotic pressure, and less commonly lymphatic obstruction. Common situations include congestive heart failure and venous obstruction (raising hydrostatic pressure), nephrotic syndrome or severe liver disease with hypoalbuminemia (lowering oncotic pressure), and occasionally malnutrition. Because the process is not driven by inflammation, capillary permeability remains largely normal, and cells are scarce in the fluid.

Clinical relevance. Transudates are most often encountered as pleural effusions, ascites, or pericardial effusions. They can cause symptoms related to the volume of fluid, such as dyspnea or abdominal distension, but they generally reflect systemic or organ-specific circulation problems rather than local infection or inflammation.

Diagnosis and analysis. Fluid analysis typically shows low protein content and low cellularity. In pleural effusions, distinguishing transudate from exudate is commonly guided by criteria such as protein and LDH ratios to serum (e.g., Light’s criteria), with transudates having lower values. Treatment focuses on addressing the underlying cause, such as managing heart failure or correcting hypoalbuminemia.