Description

Abstract

Pleural and peritoneal fluids are both ultrafiltrate of plasma that may accumulate in the chest and
abdominal cavities respectively due to changes in hydrostatic pressure, colloid/oncotic pressure,
impaired capillary permeability or impaired lymphatic drainage. The accumulated fluid may be aspirated
for therapeutic or diagnostic purposes. For pleural fluids, the differentiation between transudative or
exudative fluid using the fluid/serum protein ratio or fluid/serum lactate dehydrogenase (LDH) ratio as
defined by Lights criteria, may aid in the diagnostic process. A transudate effusion implies a change in
the balance between hydrostatic and/or oncotic pressures whereas an exudate is the active secretion
or leakage from an infected or inflamed site. The measurement of triglyceride, glucose, creatinine and
pH may aid in answering specific questions. For peritoneal or ascitic fluid, serum-ascites fluid albumin
gradient and cell count plus differential are the recommended tests in supporting a diagnosis. There
is little evidence for the measurements of amylase, tumour markers, bilirubin, cholesterol and other
analytes in pleural or peritoneal fluid.