Feline Pyothorax

Tonya E. Boyle, DVM 
Eleanor C. Hawkins, DVM, DACVIM
Standars of Care
August 2005

Pyothorax is the presence of a suppurative, septic effusion within the pleural space. It is typically easy to diagnose via cytologic analysis of fluid obtained by thoracentesis. The fluid obtained may be very turbid and can range in color from white to brown or red. Pyothorax is characterized as an exudate with protein above 3.5 g/dl, total nucleated cell count exceeding 7,000/μl of mostly degenerative neutrophils, pH below 6.9, and glucose concentration less than 10 mg/dl. Generally, extracellular and intracellular bacterial organisms are present on cytologic examination if the patient has not received antibiotic therapy before thoracentesis is performed. Because many cats with pyothorax present in respiratory distress, initial thoracentesis can be both a stabilizing, therapeutic measure as well as a definitive diagnostic test.