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Clinical Validity of a Negative Computed Tomography Scan in Patients With Suspected Pulmonary Embolism A Systematic Review

Rene Quiroz, MD, MPH; Nils Kucher, MD; Kelly H. Zou, PhD; Florian Kipfmueller, BS; Philip Costello, MD; Samuel Z. Goldhaber, MD; U. Joseph Schoepf, MD
JAMA. 2005;293(16):2012-2017. doi:10.1001/jama.293.16.2012.
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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.

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Figure 1. Posttest Probability of a Venous Thromboembolism Event After a Negative Chest Computed Tomographic Scan for Pulmonary Embolism
Graphic Jump Location

The size of each square is proportional to the precision of the estimate (number of patients, number of events, and variance). The dashed vertical line represents the overall negative likelihood ratio of 0.07.

Figure 2. Influence Analysis of Venous Thromboembolism Events
Graphic Jump Location

One study at a time was omitted from the meta-analysis. The y-axis denotes the omitted study and the reestimated negative likelihood ratio by exluding the data of that study from the analysis. The vertical dashed lines represents the overall negative likelihood ratio of 0.07.



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