What is Exudate from an Abscess Called?
The exudate from an abscess is called pus. 1
Definition and Characteristics
The term "pus" specifically refers to the purulent material that accumulates within an abscess cavity. 1, 2 This material consists of:
- Necrotic debris from liquefactive necrosis of tissue 3
- White blood cells (predominantly neutrophils) 1
- Bacteria and other infectious organisms 1, 4
- Fluid that may be clear initially but becomes turbid and purulent as infection progresses 1
Clinical Appearance and Terminology
When describing abscess contents during examination or drainage, the following terms are used based on appearance:
- "Frank pus" - the classic thick, opaque, purulent material that definitively indicates empyema or established abscess 1
- "Thin, brownish exudate" - characteristic of necrotizing fasciitis, where true pus is typically absent despite deep infection 1
- "Clear yellow fluid" progressing to "darker, more turbid, and sometimes purulent"** - describes the evolution of simple parapneumonic effusions to complicated effusions and empyema 1
Important Clinical Distinctions
Not all fluid collections contain pus. 1 The presence of frank pus distinguishes a true abscess from:
- Inflammatory masses (phlegmons) - which contain ill-defined inflammatory tissue without fluid content 1
- Simple parapneumonic effusions - which contain clear fluid with low white cell counts 1
- Seromas or hematomas - which contain serous fluid or blood rather than purulent material 1
Practical Implications
The identification of pus has direct treatment implications:
- Pus requires drainage - antibiotics alone are insufficient because the abscess environment (low pH, poor perfusion, large bacterial inocula) prevents adequate antibiotic penetration 5
- "No true pus" in necrotizing fasciitis - the absence of frank pus despite severe infection is a diagnostic feature that should not delay surgical intervention 1
- Pus culture guides therapy - obtaining pus for Gram stain and culture provides early diagnostic information and allows targeted antibiotic selection 1