Tests

1st tests to order

CBC

Test
Result
Test

Although nonspecific, normal results make a diagnosis of cellulitis less likely.[41] White cell count may also be low in patients with immunocompromising factors, such as malignancy or sepsis, although this finding is neither sensitive nor specific.[46]

Result

elevated or low white cell count

purulent focus culture and molecular diagnostic procedures

Test
Result
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.[47][48] Samples for culture and sensitivities, if indicated, should be taken before giving antibiotics.[51][52]​​

Result

growth of typical pathogen (e.g., Staphylococcus aureus)

Tests to consider

skin aspiration with culture and molecular diagnostic procedures

Test
Result
Test

Not sensitive enough for its routine use to be recommended.[13][49]

Result

growth of typical pathogen (e.g., Streptococcus pyogenes); antibiotic sensitivity

blood culture

Test
Result
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.[2]​[13]​​

Blood cultures should be obtained for patients with severe systemic features (such as high fever, tachycardia, or hypotension), and those who are immunocompromised.[2]​[13]​​

Blood for cultures should be drawn before starting antibiotic therapy.[51][52]​​

Result

growth of typical pathogen (e.g., Streptococcus pyogenes); antibiotic sensitivity

skin biopsy

Test
Result
Test

Most helpful for ruling out other causes of dermatitis in complex cases. May be helpful to confirm diagnosis in some cases.[2]​[50]​​

Result

histologic evidence of acute inflammation and presence of microorganisms

plain film x-ray

Test
Result
Test

Recommended if subjacent osteomyelitis is suspected.[54]

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
Result
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).[54][55] ​​Point-of-care ultrasonography, where available, has been shown to have good diagnostic accuracy.[56]

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
Result
Test

Indicated in evaluation of orbital and preseptal (periorbital cellulitis).[57]

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

Test
Result
Test

May be helpful if underlying osteomyelitis or necrotizing fasciitis is suspected. It should not delay surgical consultation if necrotizing fasciitis is a consideration.[54][58]

Result

contrast enhancement, thickening of deep fasciae with fluid collection in necrotizing fasciitis; evidence of osteomyelitis if present

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