Bottom line: CT chest provides greater accuracy for diagnosis of acute PE than V/Q scan. some patients may not be able to tolerate CT or have contrainidications to the test, and V/Q scan is a very reasonable alternative testing strategy. While CT has a slightly higher positive LR, the pooled sensitivity is around 86%, meaning that around 15% of patients with a PE may have a negative CT.
Summary: Pulmonary Embolism, Diagnosis section. In: DynaMed.
Based on systematic review of 12 studies that evaluated CT scan, V/Q scan or both compared to reference standard of pulmonary angiography for diagnosis of pulmonary embolism.
RESULTS: CT: Sensitivity – 86%; Specificity – 94%.
V/Q high probability scan: Sensitivity – 39%; Specificity – 97%
V/Q low probability or near-normal scan: Sensitivity – 98%; Specificity – 5%
CT and high-probability V/Q scans had similar positive LRs (14.0 and 13.2), but CT scan had better negative LR (0.15) than normal or low-probability V/Q scan (0.4 2.) However, a normal V/Q scan does have a very good negative LR (0.04, based on PIOPED I data), but this result occurs rarely.