Investigations

Patients with low or intermediate probability scans need further testing ^c , so base further investigations on the following plan ^a

V/Q scan result	PE probability	next step	d-dimer positive	d-dimer negative
normal	low and + d-dimer, moderate or high	no PE	-	-
low or intermediate	low and + d-dimer	Bilateral leg vein ultrasound positive: PE negative: no PE	-	-
low or intermediate	moderate	Bilateral leg vein ultrasound positive: PE negative: see d-dimer	Bilateral leg vein ultrasound in 1 week or venogram positive: PE negative: no PE	no PE
low or intermediate	high	Bilateral leg vein ultrasound positive: PE negative: see d-dimer	Pulmonary angiography : positive: PE;  negative: no PE	Bilateral leg vein ultrasound in 1 week or venogram positive: PE negative: no PE
high	low and + d-dimer, moderate or high	PE	-	-

Why?

• Few cases of PE are missed (0.6%: 95% CI: 0.2% to 1.4%). ^a
• 47% of patients receive no imaging, 7% undergo serial ultrasonography and 1.1% have angiography. ^a
• Patients with a non-diagnostic V/Q scan who are not anticoagulated are at increased risk of developing a PE or DVT over the next 3 months. ^c

Patients with non-diagnostic V/Q scan remain at high risk

Scan result c	Outcome	% (95% CI)
negative V/Q scan	recurrent DVT or PE at 3 months	0.7 %  (0.2% to 1.3%)
non-diagnostic V/Q scan	recurrent DVT or PE at 3 months	4.4 %  (2.7% to 5.9%)
non-diagnostic V/Q scan, leg testing negative after 14 days	recurrent DVT or PE at 3 months	1.9%  (0.8% to 3.0%)
high-probability V/Q scan	recurrent DVT or PE at 3 months	5.5%  (1.8% to 9.2%)