'Limited Negative' CTPA Results May Rule Out PE Risk

Neil Osterweil

January 13, 2015

Patients who are screened for pulmonary embolism but have a "limited negative" result on computed tomographic pulmonary angiography (CTPA) appear to be at no higher risk for a venous thromboembolism in the near future than patients who have definitively negative results, investigators say.

In a retrospective study of 2553 patients who underwent CTPA for suspicion of pulmonary emboli, the rate of false-negative results, defined as venous thromboemboli occurring within 90 days, was 1.4% for patients with a limited-negative CTPA result compared with 1.8% for patients with a definitively negative result, a difference that was not statistically significant, report Shun Yu, MD, and colleagues from the Department of Radiology and the Department of Medicine at Montefiore Medical Center and the Albert Einstein Medical College in the Bronx, New York.

"Physicians have grown accustomed to advanced CT technology with submillimeter resolution such that a 'limited' study often reflects only a minor deficiency in the usual superb image quality. A limited negative CTPA result should not be automatically interpreted as an indication of clinical uncertainty because the question of 'clinically relevant' pulmonary embolism has most likely already been answered," the authors write in a letter published online January 12 in JAMA Internal Medicine.

Although patients with a limited negative scan were at no higher risk for a subsequent venous thromboembolism, they were 4.30 times more likely than those with a definitively negative result to undergo ventilation perfusion scintigraphy and 1.47 times more likely to be started on anticoagulation therapy. There was a trend toward a higher rate of bleeding events in patients with a limited negative result, but this trend did not reach statistical significance.

To see whether clinical outcomes were similar between patients with unequivocally negative and limited negative results, the investigators reviewed records on all adults with suspected pulmonary embolism over the course of 1 year at emergency departments or inpatient sites at their centers.

They defined limited negative as a result that "reported no pulmonary embolism but also explicitly stated a limitation or qualification in the report impression."

Of the 2533 CTPA procedures performed, 264 (10%) were positive, 1663 (65%) were definitively negative, 569 (22%) were limited negative, and 57 (2%) were determined to be nondiagnostic.

As noted before, the rate of false-negatives, the primary outcome, was similar between patients with definitive and limited negative results. However, patients with limited negatives had more imaging studies with ventilation perfusion scintigraphy (odds ratio [OR], 4.30, 95% confidence interval [CI], 1.83 - 10.11) and were likely to be started on anticoagulation therapy (OR, 1.47; 95% CI, 1.17 - 1.87).

"The present study demonstrates that patients with limited negative CTPA results in which small emboli cannot be excluded have similar outcomes to those with definitively negative studies. Further diagnostic testing or initiation of anticoagulation therapy is likely unnecessary in a substantial proportion of these patients, and careful consideration of the pretest probability is warranted," the investigators write.

One coauthor disclosed that her spouse is a board member of Kryon, Bioprotect, and Orthospace. The other authors have disclosed no relevant financial relationships.

JAMA Intern Med. Published online January 12, 2015. Extract


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