Investigations

Investigations to support the clinical diagnosis of necrotising fasciitis include:

• blood tests:
  • leucocytosis
  • raised urea and creatinine
  • hypoalbuminaemia
  • acidosis
  • altered coagulation profile
• microbiology
  • send blood for culture and debrided tissues for culture and gram stain (1)
• imaging
  • plain radiography
  • soft tissue gas e.g. due to clostridial myonecrosis
  • foreign bodies
  • CT or MRI
• bedside investigations
  • “finger sweep test”
  • under local anaesthetic, a small incision is made down to the deep fascia. Gentle probing with the index finger is performed at the level of the deep fascia. A positive test is indicated when there is
    • lack of resistance to finger dissection
    • lack of bleeding
    • release of ‘dishwater fluid’ - an offensive, brown-coloured fluid
  • incisional biopsy and an immediate frozen section, culture and gram stain (2)

Remember - the diagnosis is clinical. If there is a strong clinical suspicion of the diagnosis, then urgent exploratory surgery is required - regardless of any test results.

Reference:

1. Sultan HY, Boyle AA, Sheppard N.Necrotising fasciitis. BMJ. 2012;345:e4274.
2. The Association of Anaesthetists of Great Britain and Ireland (2013). The diagnosis and management of necrotising fasciitis.
3. Shimizu T, Tokuda Y.Necrotizing fasciitis. Intern Med. 2010;49(12):1051-7.