The classification of pleural effusion (PE) can be quite challenging in practice. Veterinary medicine classifies PE into transudates, modified transudates, and exudates. Human medicine utilizes just two categories, transudates and exudates. Modified transudates are defined as closely resembling an exudate based on protein content and cellularity, but resulting from increased hydrostatic pressure. Transudates are effusions from congestive heart failure (CHF). Exudates are effusions from neoplasia, pyothorax, and FIP. Chylous effusions are classified also as exudates. This study evaluated paired samples of serum and pleural fluid in 20 cats with PE for the following parameters: Light’s criteria –pleural fluid lactate dehydrogenase concentration (LDHp), pleural fluid/serum LDH ratio, pleural fluid/serum total protein ratio (TPr), pleural fluid total protein, pleural fluid cholesterol concentration, pleural fluid/serum cholesterol ratio (CHOLr), serum-effusion cholesterol gradient (CHOLg), PE total nucleated cells count (TNCCp), and pleural fluid glucose (GLUp). In this study, nine effusions were transudates, all the result of CHF, and 11 effusions were exudates (five caused by malignancy, three by chylothorax, and three by infectious disease). Measurement of LDHp and measurement of TPr allowed reliable classification of PEs into either transudates or exudates. Calculation of CHOLr, CHOLg, and TNCCp may help classify an exudate when there is conflict between the clinical picture and laboratory results. Measurement of serum albumin when there is a transudate may provide more information regarding the pathogenesis of the effusion. [VT]
Hotz CS, Templeton SJ, Christopher MM. Comparative analysis of expert and machine-learning methods for classification of body cavity effusions in companion animals. J Vet Diagn Invest. 2005 Mar;17(2):158-64.