Investigations

• Consider d-dimer ^a in clinically low-risk patients ^{a c}

Why?

A negative d-dimer rules out a DVT in clinically low-risk patients

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
suspected deep vein thrombosis and clinical low-risk a (pre-test probability: 3%)	deep vein thrombosis (venogram and follow-up)	positive whole blood assay d-dimer	5.2 (4.0 to 6.7)	14%	0.14 (0.072 to 0.30)	0.43%

Note:

• D-dimer test characteristics vary greatly. ^a
• ELISA studies are best excluding DVT, but take several hours. ^a
• Whole blood agglutination studies can be done at the bed-side and are simple and quick to perform and read, but are less good at excluding DVT. ^a