Clinical features

• hypotension (systolic bp < 90 mmHg) ^c  
• bullae ^c  
• necrotic skin ^c  
• upper extremity affected ^c  
• crepitus ^c
• sensation loss ^c
• severe pain ^c

Why?

Intravenous drug misuse and a history of hepatitis can help diagnose necrotising fasciitis.

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
admitted to hospital with soft tissue infection c (pre-test probability:9%)	necrotising fasciitis (surgery, follow-up)	a 'hard' sign: bullae, hypotension, necrotic sign, gas on X-ray	5.5 (3.1 to 10)	34%	0.66 (0.50 to 0.87)	6%
		recent illicit drug injection	2.4 (1.8 to 3.3)	21%	0.45 (0.27 to 0.75)	4%
		upper limb affected	2.8 (1.8 to 4.4)	21%	0.62 (0.44 to 0.88)	6%