What is the workup for cellulitis?

From the Guidelines

The workup for cellulitis should begin with a thorough clinical examination to identify the characteristic signs of erythema, warmth, swelling, and tenderness, and typically does not require routine cultures of blood or cutaneous aspirates, biopsies, or swabs 1. The diagnosis of cellulitis is primarily clinical, based on the presence of signs such as erythema, warmth, swelling, and tenderness.

• Blood tests, including complete blood count, C-reactive protein, and erythrocyte sedimentation rate, may be ordered to assess the severity of infection and systemic involvement, but are not necessary for all patients.
• Blood cultures are recommended for patients with severe infection, immunocompromised status, or systemic symptoms like fever, as well as for those with malignancy on chemotherapy, neutropenia, severe cell-mediated immunodeficiency, immersion injuries, and animal bites 1.
• Imaging studies such as ultrasound or MRI may be necessary to rule out deeper infections like abscess or necrotizing fasciitis, especially if there's poor response to initial treatment.
• Empiric antibiotic therapy should be started promptly, typically with an antimicrobial agent that is active against streptococci, such as cephalexin or clindamycin, for 5 days, but treatment should be extended if the infection has not improved within this time period 1.
• For more severe infections, or those with systemic signs of infection, consider broader antibiotic coverage, including vancomycin or another antimicrobial effective against both MRSA and streptococci 1.
• Elevation of the affected limb and pain management are important supportive measures.
• The choice of antibiotics should be guided by local resistance patterns and adjusted based on culture results when available.
• Patients should be monitored for improvement within 48-72 hours, and treatment failure should prompt reassessment for complications or alternative diagnoses.

From the Research

Diagnosis of Cellulitis

• Cellulitis is an acute infection of the dermal and subcutaneous layers of the skin, often occurring after a local skin trauma 2.
• The diagnosis of cellulitis is based on the history of present illness and physical examination, and lacks a gold standard for diagnosis 3.
• Clinical presentation with acute onset of redness, warmth, swelling, and tenderness and pain is typical 3.

Differential Diagnosis

• Cellulitis can be difficult to diagnose due to a number of infectious and non-infectious clinical mimickers such as venous stasis dermatitis, contact dermatitis, eczema, lymphedema, and erythema migrans 3.
• Other dermatologic diseases that can present with similar findings to cellulitis include deep vein thrombosis and panniculitis 2.
• Undertaking a holistic patient assessment, skin assessment and thorough clinical history is important in the diagnosis of cellulitis 4.

Laboratory Tests

• Microbiological diagnosis is often unobtainable due to poor sensitivity of culture specimens 3.
• Blood cultures can be useful in the diagnosis of cellulitis in elderly patients, especially in patients with shaking chills or leukocytosis 5.
• Two routine sets of blood cultures are recommended for the precise diagnosis and appropriate treatment of cellulitis in elderly patients 5.

Management

• Most patients can be treated as an outpatient with oral antibiotics, with dicloxacillin or cephalexin being the oral therapy of choice when methicillin-resistant Staphylococcus aureus is not a concern 2.
• The majority of non-purulent, uncomplicated cases of cellulitis are caused by β-hemolytic streptococci or methicillin-sensitive Staphylococcus aureus, and appropriate targeted coverage of this pathogen with oral antibiotics such as penicillin, amoxicillin, and cephalexin is sufficient 3.