Which lab tests should be considered in patients presenting with moderate to severe cellulitis and/or systemic symptoms?

Updated: Jun 14, 2019
  • Author: Thomas E Herchline, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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The following laboratory tests may be considered in patients who present with moderate to severe cellulitis and/or systemic symptoms.

A complete blood cell (CBC) count often shows leukocytosis in the setting of severe disease; leukopenia may also be present in severe disease, especially in cases of toxin-mediated cellulitis.

The erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) level are also frequently elevated, especially in patients with severe disease requiring prolonged hospitalization. [61]

In most cases of cellulitis, blood cultures are neither necessary nor cost-effective, [9, 66] but they should be performed in patients with moderate to severe disease, [2] such as patients with cellulitis complicating lymphedema, [3] because the prevalence of bacteremia is higher in these individuals. Blood cultures are also recommended for cellulitis of specific anatomic sites, such as facial and especially ocular areas; in patients with a history of contact with potentially contaminated water; [4] , in patients with malignancy on chemotherapy, neutropenia, or severe cell-mediated immunodeficiency; and in patients with animal bites.

Gram stain, 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.

If recurrent episodes of cellulitis are suspected to be secondary to tinea pedis or onychomycosis, mycologic investigations are advisable .

Creatinine levels may be helpful to assess baseline renal function in order to correctly prescribe antimicrobial agents.

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