Clinical features

Clinical prediction rule to rank DVT risk

Ask about	Score
Active cancer (on-going treatment, diagnosed within the last 6 months or having palliative care)	+1
Paralysis, paresis, or plaster immobilisation of a leg	+1
Recently bedridden >3 days or major surgery within past 4 weeks	+1

Look for	Score
Localised tenderness over distribution of the deep veins a	+1
Entire leg swollen	+1
Calf circumference 10 cm below tibial tuberosity >3cm greater than other calf	+1
Pitting oedema only in the symptomatic leg a	+1
Collateral dilated (but not varicose) veins	+1
An alternative diagnosis as or more likely than DVT	-2

Match the patient's score to their risk.

Score a	Risk of DVT
3 or more	High
1 to 2	Moderate
0 or less	Low

Remember DVT cannot be safely diagnosed or excluded on history and physical examination alone. Imaging studies are necessary.  ^a  

Why?

When combined with ultrasonography (see below):

• Few cases of DVT are missed (0.6%). ^a If all suspected cases have ultrasound scanning only, then 5% of DVT are missed. ^a If all suspected cases have venography only, then 2% of DVT are missed. ^c
• Few patients require a venogram (5.6%) However one in three will have an extra hospital visit for additional testing. ^a
• It helps clinicians agree about the risk of DVT. K _{interobserver} for prediction rule = 0.75 (2 nurses and 2 doctors) ^a

A clinical prediction rule can help rank a patient for risk of deep vein thrombosis

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability
suspected deep vein thrombosis a (pre-test probability: 16%)	deep vein thrombosis (ultrasound, venogram, follow-up)	score: 3 or more	15 (9.5 to 25)	75%
		score: 1 to 2	1.0 (0.76 to 1.4)	17%
		score: 0 or less	0.16 (0.091 to 0.30)	3%