investigations

Last reviewed 01/2018

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 eg 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)

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.