Vetnews August 2023: Effusion fluid analysis - specific effusions

Introduction

Effusions are abnormal fluid accumulations in the peritoneal, pleural, or pericardial cavities. Many effusions are formed by passive transudation secondary to changes in hydrostatic and/or oncotic pressure (transudates) or by active exudation secondary to inflammation (exudates). Classifying an effusion as a transudate or exudate is useful to guide further diagnostics, and, in some cases, a specific diagnosis can be made (e.g. if infectious agents are visualised microscopically). However, some effusions are not accurately classified using the traditional fluid classification criteria of total protein concentration and total nucleated cell count (TNCC).