Context The clinical validity of using computed tomography (CT) to diagnose
peripheral pulmonary embolism is uncertain. Insufficient sensitivity for peripheral
pulmonary embolism is considered the principal limitation of CT.
Objective To review studies that used a CT-based approach to rule out a diagnosis
of pulmonary embolism.
Data Sources The medical literature databases of PubMed, MEDLINE, EMBASE, CRISP,
metaRegister of Controlled Trials, and Cochrane were searched for articles
published in the English language from January 1990 to May 2004.
Study Selection We included studies that used contrast-enhanced chest CT to rule out
the diagnosis of acute pulmonary embolism, had a minimum follow-up of 3 months,
and had study populations of more than 30 patients.
Data Extraction Two reviewers independently abstracted patient demographics, frequency
of venous thromboembolic events (VTEs), CT modality (single-slice CT, multidetector-row
CT, or electron-beam CT), false-negative results, and deaths attributable
to pulmonary embolism. To calculate the overall negative likelihood ratio
(NLR) of a VTE after a negative or inconclusive chest CT scan for pulmonary
embolism, we included VTEs that were objectively confirmed by an additional
imaging test despite a negative or inconclusive CT scan and objectively confirmed
VTEs that occurred during clinical follow-up of at least 3 months.
Data Synthesis Fifteen studies met the inclusion criteria and contained a total of
3500 patients who were evaluated from October 1994 through April 2002. The
overall NLR of a VTE after a negative chest CT scan for pulmonary embolism
was 0.07 (95% confidence interval [CI], 0.05-0.11); and the negative predictive
value (NPV) was 99.1% (95% CI, 98.7%-99.5%). The NLR of a VTE after a negative
single-slice spiral CT scan for pulmonary embolism was 0.08 (95% CI, 0.05-0.13);
and after a negative multidetector-row CT scan, 0.15 (95% CI, 0.05-0.43).
There was no difference in risk of VTEs based on CT modality used (relative
risk, 1.66; 95% CI, 0.47-5.94; P = .50).
The overall NLR of mortality attributable to pulmonary embolism was 0.01 (95%
CI, 0.01-0.02) and the overall NPV was 99.4% (95% CI, 98.7%-99.9%).
Conclusion The clinical validity of using a CT scan to rule out pulmonary embolism
is similar to that reported for conventional pulmonary angiography.