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Laboratory Tests and Ancillaries
Gram Stain, Culture and Sensitivity
The etiology of cellulitis remains unidentified in most patients and treatment needs to be empiric based on clinical presentation.
Lesion Culture
Cultures of aspirate, biopsy and blood specimens in adults without comorbid conditions yield low results and are generally not indicated. This is essential only for those with a history of malignancy or immunosuppression, recurrent or multiple abscess, treatment failure with the initial antibiotic regimen, patients with systemic complications (ie pyrexia, hypotension), predisposing factors (ie immersion injury, animal bites, neutropenia), severe local infection, indication for prophylaxis of infective endocarditis and living in areas with increased S aureus susceptibility patterns. Fine-needle aspiration of closed lesions gives positive results approximately 30% of the time. This technique may be useful when unusual pathogens are suspected (eg immunocompromised patients), when fluctuant areas are detected or when initial antimicrobial therapy has failed. If a specimen can be taken from the site of origin of the cellulitis, a positive culture can be obtained in about 1/3 of the patients.
Blood Cultures (BC)
Cellulitis Erysipelas_Diagnostics
Blood cultures are useful only in patients with significant leukocytosis, severe systemic symptoms, underlying comorbidities, cellulitis complicating lymphedema, buccal or periorbital cellulitis, persistent/recurrent cellulitis, certain exposures (water-related injury or animal bites) and in elderly or immunocompromised patients.
Serologic Testing
Patients with a history of recurrent cellulitis may benefit from serologic assays such as anti-streptolysin-O (ASO) reaction, antideoxyribonuclease B test (anti-DNAse B), anti-hyaluronidase test (AHT), or Streptozyme.
Imaging
Imaging studies are not necessary in most cases. A computed tomography (CT) or magnetic resonance imaging (MRI) may be requested for suspected necrotizing fasciitis. Radiographic exams may be used to rule out osteomyelitis and other diseases that may be secondary to underlying comorbidities.