Investigations

• Impedance plethysmography ^a though this is less good than ultrasonography. ^a

• Ultrasound scanning is better than IPG at diagnosing and excluding DVT in patients with symptoms. ^a
• There are fewer uninterpretable scans using ultrasound ^a though the study used has no clear effect on recurrent venous thromboembolism or death. ^a

More ultrasound scans are interpretable than impedance plethysmography

Patient	Treatment	Comparison	Outcome	CER	RRR (95% CI)	NNT (95% CI)
suspected DVT a	impedance plethysmography	ultrasound scan	uninterpretable non-invasive test or venogram at 8 days	4.5%	55% (5% to 78%)	41 (21 to 440)