Computed Tomography for Diagnosing Pulmonary Embolism

Health Technology Assessment Committee Findings

  1. Pulmonary embolism (PE) is associated with high mortality (as much as 30% if left untreated) and risk of other serious complications. Computed Tomography (CT) is the optimal method of diagnosing PE from a clinical and cost-effectiveness perspective; however, if used inappropriately, the use of CT in diagnosing a possible PE puts patients at higher risk of radiation exposure and unnecessary treatment, and costs the health system money that could be better spent elsewhere.
  2. Risk stratification tools have been developed that, while cannot be used to diagnose PE, can be used to help determine the clinical probability of PE. These tools include the Wells’ criteria, the revised Geneva (rGeneva) score, and the Pulmonary Embolism Rule out Criteria (PERC). In addition, a negative D-dimer blood test can assist when trying to rule out PE.
  3. A systematic review of the literature found fourteen studies on strategies to support more appropriate use of CT. Studies were of low to moderate quality and there is uncertainty in pooled results; however, in the absence of additional literature, this evidence suggests that use of the Wells’ criteria and D-dimer test in the diagnostic pathway are effective in reducing the number of unnecessary CT examinations, with the use of Clinical Decision Support (CDS) tools the most likely to improve the CT yield1. No evidence was found on rGeneva; evidence on the use of PERC was found in guidelines.
  4. Cost-effectiveness analysis suggests the percentage of patients receiving CT examinations for PE in BC emergency room departments could be reduced by a third and up to one half with the introduction of CDS tools, without significantly impacting the health of patients:
    Strategy Cost ICUR QALYs CT Yield %CT FP FN
    Wells → PERC → D-dimer → CT* $1,981 - 12.489 21.1% 48.3% 3.0% 1.7%
    Wells → D-dimer → CT (moderate and high)** $2,193 $30,000 12.496 17.0% 71.6% 4.4% 1.5%
    Clinical judgement and CT alone*** $2,558 $364,900 12.497 14.2% 100.0% 6.4% 1.4%

    ICUR=Incremental Cost-utility Ratio; QALYs=Quality of Life Years; CT yield= % CT examinations positive for PE whether true positive or false positive; %CT=% patients receiving a CT; FP=False Positive; FN=False Negative

    * All patients who have a high Wells’ score go directly to CT, all patients with a moderate Wells’ score have D-dimer and positive D-dimer go to CT, all patients with a low Wells’ score have a PERC test, negative PERC tests are no longer suspected of PE, positive PERC tests have D-Dimer and positive D-Dimer go to CT

    ** All patients who have a high or moderate Wells’ score go directly to CT, all patients with a low Wells’ score have D-dimer, and positive D-dimer go to CT

    *** All patients suspected of PE have a CT scan
  • Wells → PERC → D-dimer → CT is expected to be the most cost-effective strategy; Wells → D-dimer → CT (moderate and high) is also a cost-effective strategy when compared with the use of clinical judgement and CT alone. Wells → D-dimer → CT is estimated to cost about $200 per patient more than Wells → PERC → D-dimer → CT but has slightly better health outcomes.
  • CT alone is more costly and shows a very high incremental cost per QALYs gained ($364,900) compared to Wells → D-dimer → CT strategy.
  • Benefits to the patient population of using either the Wells → PERC → D-dimer → CT or the Wells → D-dimer → CT diagnostic pathway will include reduced exposure to high doses of radiation, and fewer false positives (FP) and unnecessary treatment; however, there is a slightly higher risk of a missed diagnosis (false negative or FN) of those two pathways when compared to clinical judgement and CT alone.
  • Per patient health outcomes and health care diagnostic and treatment costs were considered over the lifetime of the patient, based on an estimated annual number of patients presenting in BC emergency departments with suspected PE (6,139).
  1. Budget impact analysis that extrapolated costs over one and five years suggest that implementing a CDS tool for diagnosing PE would be cost saving. The Wells → PERC → D-dimer → CT strategy could result in up to $4M in cost avoidances in the first year alone, and up to $20M over five years for all of BC. Implementing the Wells → D-dimer → CT strategy could save $800k in the first year and $4M over five years for all of BC.
  2. Developing a decision support tool is not a significant cost investment. However, compliance by physicians will affect health outcomes for patients and cost-savings; therefore, it will be important to identify health system leaders and departmental champions, and engage physicians in developing a program to achieve the necessary buy-in.

Health Technology Assessment Committee Recommendations

  1. To support the appropriate use of computed tomography (CT) to diagnose pulmonary embolism (PE), based on the available evidence, it is recommended that the diagnostic pathway include Well’s Criteria (Wells), Pulmonary Embolism Rule-out Criteria (PERC), D-dimer and CT, which has been shown to have similar clinical effectiveness to the use of CT alone but is more cost-effective.
  2. To support adoption of this diagnostic pathway, it is recommended that the Emergency Medicine Network lead the development of a clinical decision support tool, a clear pathway for patients following discharge, and targeted education for all emergency room physicians.


1 CT Yield=the percentage of CT examinations that are positive for PE, whether a true positive or false positive.