Tests
1st tests to order
CBC
Test
Although nonspecific, normal results make a diagnosis of cellulitis less likely.[36] White cell count may also be low in patients with immunocompromising factors or sepsis, although this finding is neither sensitive nor specific.
Result
elevated or low white cell count
purulent focus culture and molecular diagnostic procedures
Test
This should be performed if cellulitis is associated with, or adjacent to, a wound or pustular focus. It may help identify the presence of resistant pathogens such as MRSA and guide antibiotic selection.[37][38] Samples for culture and sensitivities, if indicated, should be taken before giving antibiotics.[34][41]
Result
growth of typical pathogen (e.g., Staphylococcus aureus)
Tests to consider
skin aspiration with culture and molecular diagnostic procedures
blood culture
Test
Not sensitive enough for its routine use to be recommended, but should be reserved for patients with more severe disease where blood cultures are more likely to yield the causative organism.[13]
Blood cultures should be obtained for patients with severe systemic features (such as high fever, tachycardia, or hypotension), and those who are immunocompromised.[13]
Blood for cultures should be drawn before starting antibiotic therapy.[34][41]
Result
growth of typical pathogen (e.g., Streptococcus pyogenes); antibiotic sensitivity
skin biopsy
Test
May be helpful to confirm diagnosis in some cases.[40]
Result
histologic evidence of acute inflammation and presence of microorganisms
plain film x-ray
Test
Recommended if subjacent osteomyelitis is suspected.[43]
Cellulitis cannot be reliably confirmed with this technique.
Result
lytic or periosteal changes in subjacent osteomyelitis or gas in subcutaneous tissue if necrotizing fasciitis is present
ultrasound
Test
Indicated if abscess is suspected (e.g., if tender fluctuance is present on examination or if there is an incomplete response to antimicrobial therapy).[43][44][45]
Cellulitis can be confirmed by this method but it is usually not necessary to make the diagnosis.
Result
fluid collection seen if abscess is present
CT scan
Test
Indicated in evaluation of orbital and preseptal (periorbital cellulitis).
Cellulitis can be confirmed by this method but it is usually not necessary to make the diagnosis, unless involving the orbital and preseptal forms.
Result
fluid collection seen if abscess is present; orbital or preseptal (periorbital) cellulitis
MRI
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