Is a Blood Culture Needed in Cellulitis?

Written by Clay Smith

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Blood cultures were low yield in patients admitted with cellulitis and should largely be avoided.  Similarly, imaging was also low yield but changed management in a minority of cases.

Why does this matter?
The IDSA recommends blood culture in patients with cellulitis only if immunocompromised, having systemic effects likely from a toxin-producing organism, or those with animal bites.  Likewise, imaging is recommended by the IDSA only in those with cellulitis and febrile neutropenia.  So how does this work out in actual practice?

Go with IDSA for blood culture in cellulitis but maybe not for imaging
This was a retrospective, single center study of patients admitted with cellulitis.  Of the 183 patients, 60 had blood cultures; one was positive but did not change management.  Eighteen were IDSA-appropriate cultures. Imaging of all sorts was obtained on 124/183 (68%) and included ultrasound, x-ray, CT, and MRI.  None of the imaged patients had febrile neutropenia.  In eight cases, imaging changed management.  Diagnoses on imaging included hematoma, abscess, and osteomyelitis.  MRI was helpful in 4 of 11 cases.  My take home from this is that blood cultures may largely be omitted in patients with cellulitis.  And imaging is often unhelpful in changing management.  But I think the IDSA guideline that it should only be done in patients with febrile neutropenia is shortsighted.  It is often difficult to know if an abscess is present without ultrasound, especially in IV drug abusers.  Also, it can be very reassuring if x-ray or CT does not show soft-tissue gas in some cases in which deep soft tissue or necrotizing infection is in the differential.  So I am not ready to ditch imaging in select cases, but this shows me that it will often be low yield.  In another review of this article, Radecki also thought the conclusions may have been overstated.

Source
Clinical Usefulness of Imaging and Blood Cultures in Cellulitis Evaluation.  JAMA Intern Med. 2018 Apr 2. doi: 10.1001/jamainternmed.2018.0625. [Epub ahead of print]

Peer reviewed by Thomas Davis

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