Pulmonary Embolism

Numbers (% or LR)
Incidence
General Population0.27%
ER population with concern for PE/DVT (Wells)1.3%
Risk Factor
1. Cancer LR 2.5
2. Recent surgery / immobility LR 3.0
Symptoms/Syndrome
1. PE #1 clinical diagnosis LR 5.0
2. Tachycardia (>100)LR 3.0
3. Signs/Sx of DVT (unilateral edema, leg pain)LR 5.0
4. Hemoptysis LR 2.5
5. Previous PE LR 3.0
6. No clinical symptoms or syndrome LR 0.8
TestClinical sensitivityClinical specificity
1. CT PE90% 92%
2. D-dimer97% 40%
Other
Explanation for + test without disease:
Subsegmental PEs would not have been identified by angiogram in PIOPED. Anticoagulation of uncertain benefit in these patients. CT scan artifact/contrast issue.
Explanation for - test with disease:
Small PE or one that cannot be detected because of location in vasculature.
Example of high value use:
Testing patients with appropriate syndromes who can receive anticoagulation.
Example of low value use:
Testing all ER patients with respiratory problems. Reflex CTPE on any patients with + D-dimer testing.

Discussion

Incidence and risk factors:

Pretest probability for PE was derived from the Wells’ and Geneva scores. These group risk into low, medium and high with a score translating to 3 specific probabilities (e.g. 1.3%, 16%, 41% for Wells’). The implied LR generally match with the risk levels but provide risk along a continuum instead of ordinal outcomes. Differences between scores were resolved with expert adjudication.

Incidence in the general population was derived as follows, the American Lung Association estimates 900,000 Americans/year have PE. The US population is 331 million in 2021, equaling an incidence of 0.27%/year. This is likely an overestimate given hospital-based PE incidence ~200,000/year in America.

To determine the sensitivity and specificity of CT PE, we used the most recent comprehensive meta-analysis which reported a pooled sensitivity of 86% and specificity of 94%.[1] However, this was performed prior to the major study, PIOPED II, which if poor image quality CT results were included, found sensitivity of 84% and specificity of 90%.[2]

Given technological advancement since these studies, experts expected CT PE would be more sensitive than 15 years ago, but perhaps no more specific.

A recent review of D-dimer for thromboembolism (DVT/PE) identified age specific specificities while sensitivity remained at or above 97% at all ages. The average specificity of 40% was chosen to reflect a mix between age and absolute cut-off D-dimer value (>500) or those that use age specific cutoffs, which are more specific in older age.[3]