ESSENTIALS: When high probability of pulmonary embolism (PE), sensitivity of 
computed tomography (CT) is unclear. We investigated the sensitivity of 
multidetector CT among 134 patients with a high probability of PE. A normal CT 
alone may not safely exclude PE in patients with a high clinical pretest 
probability. In patients with no clear alternative diagnosis after CTPA, further 
testing should be strongly considered.
BACKGROUND: Whether patients with a negative multidetector computed tomographic 
pulmonary angiography (CTPA) result and a high clinical pretest probability of 
pulmonary embolism (PE) should be further investigated is controversial.
METHODS: This was a prospective investigation of the sensitivity of 
multidetector CTPA among patients with a priori clinical assessment of a high 
probability of PE according to the Wells criteria. Among patients with a 
negative CTPA result, the diagnosis of PE required at least one of the following 
conditions: ventilation/perfusion lung scan showing a high probability of PE in 
a patient with no history of PE, abnormal findings on venous ultrasonography in 
a patient without previous deep vein thrombosis at that site, or the occurrence 
of venous thromboembolism (VTE) in a 3-month follow-up period after 
anticoagulation was withheld because of a negative multidetector CTPA result.
RESULTS: We identified 498 patients with a priori clinical assessment of a high 
probability of PE and a completed CTPA study. CTPA excluded PE in 134 patients; 
in these patients, the pooled incidence of VTE was 5.2% (seven of 134 patients; 
95% confidence interval [CI] 1.5-9.0). Five patients had VTEs that were 
confirmed by an additional imaging test despite a negative CTPA result (five of 
48 patients; 10.4%; 95% CI 1.8-19.1), and two patients had objectively confirmed 
VTEs that occurred during clinical follow-up of at least 3 months (two of 86 
patients; 2.3%; 95% CI 0-5.5). None of the patients had a fatal PE during 
follow-up.
CONCLUSIONS: A normal multidetector CTPA result alone may not safely exclude PE 
in patients with a high clinical pretest probability.