Investigations

Why?

A ventilation-perfusion scan can help diagnose or exclude a pulmonary embolism

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability
suspected pulmonary embolism a (pre-test probability: 27%)	pulmonary embolism (angiogram or follow-up)	high probability v/q scan	13 (8.1 to 19)	82%
		intermediate probability v/q scan	1.1 (0.91 to 1.3)	29%
		low probability v/q scan	0.38 (0.29 to 0.52)	12%
		normal/ near normal scan v/q scan	0.11 (0.045 to 0.26)	4%

Note:

• Around 60% of all scans are low or intermediate probability. ^a
• Pre-existing heart lung disease does not affect the accuracy of the scan, but more patients have non-diagnostic scans. ^a