Does Negative CTPA Rule Out High Pretest Probability PE?

July 30, 2018

Written by Thomas Davis

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For patients with high pretest probability for pulmonary embolism, negative CT pulmonary angiography (CTPA) alone does not appear to adequately rule out venous thromboembolism (VTE).

Why does this matter?
Current guidelines state that CTPA is sufficient to rule out PE. However, these recommendations are based on studies that predominately included patients with a low to moderate risk of PE. Among patients with a high pre-test probability of PE, is CTPA as a single test adequate to exclude VTE?

Is the one-and-done era finally over?
This was a meta-analysis of 22 prospective studies. Among the 7863 patients with an initially negative CTPA, 148 had VTE confirmed at the index visit. Another 74 patients were diagnosed with VTE during a follow-up period of generally 3 months. For the general cohort, 2.4% of patients were diagnosed with VTE at either the index visit or during follow-up. However, among patients with a high pre-test probability of PE (>40%) and a negative CTPA, VTE was ultimately confirmed in 8.1% of patients with an upper confidence limit of 14.5% (95% CI, 3.4-14.5%). While patients with high pretest probability make up a small portion of the patients we evaluate for VTE in the emergency department (<5%), it is important to identify these patients and consider additional testing since two-thirds of the VTEs were identified on the index visit. Because 76% of the VTEs identified at the index visit were DVTs following a negative CTPA, ultrasound may be useful. However, there is currently no validated diagnostic algorithm to evaluate these high risk patients.

Source
Outcomes following a negative computed tomography pulmonary angiography according to pulmonary embolism prevalence: a meta-analysis of the management outcome studies.  J Thromb Haemost. 2018 Jun;16(6):1107-1120. doi: 10.1111/jth.14021. Epub 2018 May 17.
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Another Spoonful
Don’t miss the excellent and entertaining discussion of this article by Ryan Radecki on EM Lit of Note.  Journal Watch had a free summary of this as well.

Reviewed by Clay Smith