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Practice Uncertainties

What diagnostic strategies can help differentiate cellulitis from other causes of red legs in primary care?

BMJ 2020; 368 doi: (Published 12 February 2020) Cite this as: BMJ 2020;368:m54
  1. George Edwards, research assistant1,
  2. Karoline Freeman, research fellow2,
  3. Martin J Llewelyn, professor3,
  4. Gail Hayward, associate professor1
  1. 1Nuffield Department of Primary Care Health Sciences, Radcliffe Observatory Quarter, Oxford, UK
  2. 2Warwick Medical School, Division of Health Sciences, University of Warwick, Coventry, UK
  3. 3Brighton and Sussex Medical School, University of Sussex, UK
  1. Correspondence to G Hayward gail.hayward{at}

What you need to know

  • Red legs owing to non-infectious causes are often misdiagnosed as cellulitis, resulting in unnecessary antibiotics and hospitalisation

  • Novel approaches such as thermal imaging, clinical prediction models, point-of-care tests, and a visually based computerised diagnostic decision support system could potentially aid the diagnosis of cellulitis, but there is very limited and weak evidence to support their use in primary care

  • Clinically, a unilateral presentation increases the odds of cellulitis, and lack of elevated temperature compared with the unaffected limb can help rule out cellulitis

Cellulitis is the most common bacterial infection causing red legs. It is treated with antibiotics, and patients with severe disease may need to be hospitalised.1234 In 2017-18, 317 522 patients were given a diagnosis of cellulitis in UK hospitals.5 The true incidence, including patients managed through primary care, is likely to be higher.

Redness is often accompanied by other classic signs of inflammation: tenderness, warmth, and swelling. Other causes of red legs can present with some, or all, of these common symptoms6 (table 1). These conditions may be misdiagnosed as cellulitis. Studies in US emergency departments have reported that between 28% and 30.7%789 of cellulitis diagnoses are incorrect. Misdiagnosis can result in unnecessary antibiotic treatment10 and hospitalisation. Conversely, untreated cellulitis can have complications such as extensive tissue damage and necrosis, disseminated infection, septic shock, and potentially death.11Figures 1 and 2 show alternative diagnoses for red legs.

View this table:
Table 1

Distinguishing cellulitis from other causes of red legs. Major alternatives to consider and diagnostic considerations, adapted from clinical guidelines124

Fig 1

Alternative diagnoses of red legs: (a) cellulitis, (b) varicose eczema, (c) deep vein thrombosis, (d) gout

Fig 2

Concurrent cellulitis and deep vein thrombosis. The manifestation of skin diseases can vary between ethnic groups and skin colours

Differentiating red legs …

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