transudate

Transudate is a noninflammatory, acellular fluid that forms as an ultrafiltrate of plasma. It accumulates in body cavities or tissues when systemic factors cause imbalances in hydrostatic or oncotic pressures. In contrast to exudates, transudates have low protein content, low LDH, few cells, and are usually clear.

Formation mechanisms include increased capillary hydrostatic pressure (for example heart failure, volume overload, constrictive pericarditis, portal hypertension) and decreased plasma oncotic pressure (for example hypoalbuminemia from nephrotic syndrome, liver cirrhosis, malnutrition). Normal vascular permeability is maintained, which keeps the fluid relatively protein-poor.

Transudates commonly accumulate in pleural, peritoneal, and pericardial spaces, producing pleural effusions, ascites, or pericardial effusions. Common systemic conditions associated with transudates are congestive heart failure, cirrhosis with ascites, nephrotic syndrome, and generalized edema from hypoalbuminemia.

Diagnosis and differentiation from exudates rely on comparative protein and LDH content. Transudates have lower protein and LDH than plasma, whereas exudates show elevated levels; in pleural fluid, this distinction is often assessed with methods such as Light's criteria.

Management focuses on treating the underlying cause and correcting the hemodynamic or oncotic imbalances, for example by diuretics for volume overload, salt restriction, and therapies for liver or kidney disease.