Cellulitis laboratory tests

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Aditya Govindavarjhulla, M.B.B.S.

Overview

When cellulitis is accompanied by signs and symptoms of systemic toxicity (e.g., fever or hypothermia, tachycardia, and hypotension), blood samples should be collected for culture with susceptibility tests, complete blood cell count with differential, creatinine, bicarbonate, creatine phosphokinase, and C-reactive protein levels. A definitive etiologic diagnosis by means of needle aspiration or punch biopsy may be considered in the presence of elevated serum creatinine, decreased serum bicarbonate, elevated creatine phosphokinase, marked left shift, or C-reactive protein >13 mg/L.

Laboratory Findings

Blood tests

• Total blood count increases. Leukocytosis is seen in most of the cellulitis cases, but in a few toxin mediated cellulitis cases leucopenia may be observed.
• ESR and CRP can be used as prognostic indicators. New recommendations are more favorable towards the use of CRP compared to ESR as an indicator of infection severity. Elevated ESR and CRP levels on admission are associated with a longer hospitalization period.
• If repeated infections of cellulitis occur, diabetes should be ruled out as a cause. Blood glucose levels will assist in determining if diabetes has had any influence on the development of cellulitis.

Staining and cultures

• Blood cultures are warranted in the following conditions:

• Accompanying signs and symptoms suggestive of bacteremia (e.g., high fever, chills, hypothermia, tachycardia, and hypotension)
• Buccal cellulitis
• Periorbital cellulitis
• Cellulitis superimposed on lymphedema
• When a salt-water or fresh-water source of infection is likely

• Blood cultures are positive only in few cases of mild infection and community acquired cellulitis. Blood cultures become a significant diagnostic tool when the inflammation present in cellulitis spreads systemically.
• In cases where an abscess has formed, gram staining and cultures of the drained fluid may be helpful in further management of the condition.
• In cases of recurring cellulitis of the foot, fungal infections have to be ruled out. Skin scrapings will be helpful for the diagnosis.

Drug Resistance

• Microbial resistance to drugs is a very common and serious problem. In cases of non resolution, severe infections leading to hospitalization drug sensitivity has to be tested.

Gallery

• Gram-negative Haemophilus influenzae bacteria, which were cultured on chocolate agar medium (10x mag). From Public Health Image Library (PHIL). [7]

  Gram-negative Haemophilus influenzae bacteria, which were cultured on chocolate agar medium (10x mag). From Public Health Image Library (PHIL).