Are normal results on imaging technique (CTPA) safe to rule out blood clot in the lung?

By Nadia Arshad, PhD in TREC

Multidetector Computed Tomographic Pulmonary Angiography (MD CTPA) is an imaging technique used to diagnose pulmonary embolism (blood clots in the lung).

Embolism - Diagnosis on the Display of Medical Tablet and a Black Stethoscope on White Background.

A study accepted for publication in Journal of Thrombosis and Hemostasis on the 1st of November 2015, discussed whether negative (normal) results on CTPA can safely rule out pulmonary embolism in patients with already high clinical suspicion. High clinical suspicion means those who have signs and symptoms suggestive of pulmonary embolism together with clinical risk factors for pulmonary embolism. Clinical suspicion is assessed by a scoring system called Wells criteria. Using these criteria, various signs, symptoms and risk factors for pulmonary embolism are given a predefined number of points and then summarized to yield a total Wells score.

This study was conducted in Madrid, Spain. A total of 134 cases (aged 20-95 years) with high clinical suspicion (Wells score ≥7) and normal results on imaging technique (CTPA) were enrolled in this study. The authors found that the possibility of the CTPA imaging technique to correctly detect blood clots in the lung was 98%, and that the chances of being disease-free with normal results on the CTPA imaging technique was 95%. Patients with high clinical suspicion without an alternative diagnosis, who were not further tested nor treated after a normal CTPA, had a 5-times higher rate of pulmonary embolism recurrence than those with a low clinical suspicion. This may suggest further testing among those with a high clinical suspicion when other diseases causing the same symptoms are unlikely.

The authors of this study concluded that normal results on CTPA imaging technique alone may not be safe and sufficient to exclude blood clots in the lung in patients with already high clinical suspicion. In patients with no clear alternative diagnosis after CTPA, further testing should be considered.


Moores L, Kline J, Portillo AK, Resano S, Vicente A, Arrieta P, et al. Multidetector computed tomographic pulmonary angiography in patients with a high clinical probability of pulmonary embolism. J Thromb Haemost. 2015

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