In general, no workup is required in uncomplicated cases of cellulitis that meet the following criteria:
Limited area of involvement
No systemic signs of illness (eg, fever, chills, dehydration, altered mental status, tachypnea, tachycardia, hypotension)
No risk factors for serious illness (eg, extremes of age, general debility, immunocompromised status)
According to guidelines from the Infectious Diseases Society of America (IDSA), cultures of blood or cutaneous aspirates, biopsies, or swabs are not routinely recommended in patients with cellulitis. The IDSA recommends bloodwork for patients with soft-tissue infection who have signs and symptoms of systemic toxicity; such tests include blood cultures, complete blood cell count (CBC) with differential, and levels of creatinine, bicarbonate, creatine phosphokinase, and C-reactive protein (CRP).
The IDSA recommends considering inpatient admission in the presence of hypotension and/or the following laboratory findings: an elevated creatinine level, an elevated creatine phosphokinase level (two to three times the upper limit of normal), a CRP level > 13 mg/L (> 123.8 mmol/L), a low serum bicarbonate level, or a marked left shift on the CBC with differential.
A CBC often shows leukocytosis in the setting of severe cellulitis; leukopenia may also be present in severe disease, especially in cases of toxin-mediated cellulitis. The ESR and CRP level are also frequently elevated, especially in patients with severe disease requiring prolonged hospitalization.
Gram staining, whether obtained via biopsy or aspiration of the infected area, has a low yield and is unnecessary in most cases, unless purulent material is draining or bullae or abscess is present.
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Cite this: Michael Stuart Bronze. Fast Five Quiz: Cellulitis Key Aspects - Medscape - Jan 23, 2020.