Laboratory Testing for Suspected Wound Infection
For suspected wound infection, obtain a tissue biopsy from the advancing margin of the lesion for culture (with Gram stain), and blood cultures if there are signs of systemic infection. 1, 2
Core Laboratory Tests
Wound Culture Specimen Collection
Tissue biopsy is the gold standard and should be obtained from the advancing margin of the lesion, not from pus or necrotic tissue 1, 2
Thoroughly cleanse the wound and remove all topical antimicrobials before specimen collection, as these can affect culture results 1, 3
Avoid surface swabs as they are inadequate and do not represent the true disease process—they only capture surface flora rather than the pathogens in deeper tissue 1, 2
Request both aerobic and anaerobic cultures, particularly for bite wounds and deep tissue infections 2
Request a Gram stain to assess for indicators of inflammation (neutrophils), superficial contamination (squamous epithelial cells), and microorganisms 1
Blood Cultures
Obtain blood cultures when there are signs of systemic infection including fever, elevated white blood cell count, or signs of sepsis 3, 4
Blood cultures should always be collected for burn wound infections to detect systemic disease secondary to the wound 1, 3
The yield of blood cultures in skin and soft tissue infections without systemic signs is low (7.0%), so they are not routinely indicated in uncomplicated cases 4
Specific Wound Type Considerations
Burn Wounds
Request quantitative culture (either tissue biopsy or surface swab) to monitor bacterial colonization 1, 3
Quantitative tissue biopsy culture should be supplemented with histopathological examination to assess the extent of microbial invasion 1, 3
If using surface swabs, perform twice-weekly sampling of the same site to monitor trends in bacterial colonization 3
Confirm your laboratory offers quantitative cultures before specimen collection, as not all facilities provide this service 1, 3
Bite Wounds (Human or Animal)
Collect tissue or aspirate specimens for both aerobic and anaerobic cultures, as these infections are typically polymicrobial 2
Swabs are particularly inadequate for bite wounds due to the polymicrobial nature and need to identify both aerobic and anaerobic pathogens 1
Trauma-Associated Wounds
Do not submit specimens for culture within the first 48 hours post-trauma, as growth likely represents environmental contamination rather than true infection 2
The optimal time to obtain cultures is immediately post-debridement of the trauma site 2
Critical Specimen Labeling
Be specific about body site and type of wound on the laboratory requisition (e.g., "human bite wound, knuckle" rather than just "wound") 1, 3
Do not request the laboratory to "report everything that grows", as this leads to confusion between colonization and true infection 1, 3
Common Pitfalls to Avoid
Relying on swab cultures alone: Surface swabs capture colonizing organisms and contaminants, not the true pathogens causing deep tissue infection 1, 2, 5
Failing to cleanse the wound properly: Topical antimicrobials and debris must be removed before sampling to avoid false-negative results 1, 3
Treating all cultured organisms: When multiple organisms grow (especially 8 or more), this strongly suggests contamination rather than true infection—focus treatment on the most virulent pathogens like S. aureus and β-hemolytic streptococci 5
Obtaining blood cultures in all cases: Blood cultures have low yield (7.0%) in patients without systemic signs and are not cost-effective in uncomplicated skin and soft tissue infections 4
Additional Laboratory Tests
While not microbiological tests, consider obtaining:
Complete blood count (CBC) to assess for leukocytosis as a marker of systemic infection 3
Inflammatory markers (ESR, CRP) may support the diagnosis of infection, though these are nonspecific
Blood glucose in diabetic patients, as hyperglycemia impairs wound healing and increases infection risk