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

Harvard University, Cambridge, Massachusetts, United States
JAMA The Journal of the American Medical Association (Impact Factor: 35.29). 05/2005; 293(16):2012-7. DOI: 10.1001/jama.293.16.2012
Source: PubMed


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.
To review studies that used a CT-based approach to rule out a diagnosis of pulmonary embolism.
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.
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.
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.
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%).
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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Available from: Uwe Joseph Schoepf
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    • "A meta-analysis by Quiroz et al. with pooled results involving 15 studies and 3,500 patients with suspected PE suggested that clinical outcome is not adversely affected if anticoagulant therapy is withheld based on a negative CT scan with a negative predictive value of 99.1 % [45]. These studies were performed with older generation MDCT systems, and it is therefore possible that subsegmental pulmonary emboli remained undetected. "
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    ABSTRACT: Acute pulmonary embolism (PE) is diagnosed either by ventilation/perfusion (V/P) scintigraphy or pulmonary CT angiography (CTPA). In recent years both techniques have improved. Many nuclear medicine centres have adopted the single photon emission CT (SPECT) technique as opposed to the planar technique for diagnosing PE. SPECT has been shown to have fewer indeterminate results and a higher diagnostic value. The latest improvement is the combination of a low-dose CT scan with a V/P SPECT scan in a hybrid tomograph. In a study comparing CTPA, planar scintigraphy and SPECT alone, SPECT/CT had the best diagnostic accuracy for PE. In addition, recent developments in the CTPA technique have made it possible to image the pulmonary arteries of the lungs in one breath-hold. This development is based on the change from a single-detector to multidetector CT technology with an increase in volume coverage per rotation and faster rotation. Furthermore, the dual energy CT technique is a promising modality that can provide functional imaging in combination with anatomical information. Newer high-end CT scanners and SPECT systems are able to visualize smaller subsegmental emboli. However, consensus is lacking regarding the clinical impact and treatment. In the present review, SPECT and SPECT in combination with low-dose CT, CTPA and dual energy CT are discussed in the context of diagnosing PE.
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    • "The consequences of missing the diagnosis and the ease of recalling prior serious cases may lead to an overestimation of the probability of PE and lower the threshold for initiating a cascade of diagnostic testing, a phenomenon described as the availability heuristics in cognitive psychology [7] [8]. The widespread round-theclock availability, excellent accuracy [9] [10] of CT pulmonary angiography (CTPA), and ability to provide an alternative diagnosis [11] [12] may further lower the threshold for performing this imaging study and result in its overuse. On the other hand, outcome studies using clinical prediction rules to refine diagnostic certainty have shown that PE can be safely excluded in patients with low clinical probability and normal d-dimer levels without an imaging study [1] [2] [5]. "
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    • "There is actually a conclusive evidence that MDCT scan if positive provides reliable confirmation of the presence of PE and more importantly if negative rules out clinically significant PE with a high negative predictor value (99.4%).34,35 However, considering ultrasound of the lower extremities in patients with high clinical suspicion for acute PE and a negative CT would appear prudent.36,37 "
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