Tiny clots in the lung put patients at risk of future blood clots

December 16, 2021

image of blood clot in lungs“These findings really surprised us, because these clots are so small. This answers a question that experts have been debating for years,”- Dr. Marc CarrierA study led by Drs. Grégoire Le Gal and Marc Carrier found that tiny clots in the lungs are not as harmless as previously thought, and in most cases should be treated with blood thinners. These unexpected findings are set to change clinical practice. 

Due to advances in CT technology at emergency departments, more people are being diagnosed with 1-6 millimeter clots in the lung’s smaller blood vessels, known as subsegmental pulmonary embolisms. However, it wasn’t clear whether these clots were harmful, and some physicians will treat them while others will not. 

The study followed 266 patients from 18 sites who were diagnosed with these clots. The patients were followed for 90 days to see if they developed a second clot elsewhere in the body. Eight patients (3.1 percent) developed a second clot, which is much higher than the 0.1% incidence of these clots in the general population. 

The findings, published in Annals of Internal Medicine, show that patients with subsegmental pulmonary embolism are at greater risk of future blood clots, and should be treated with blood thinners.

“These findings really surprised us, because these clots are so small. This answers a question that experts have been debating for years,” said Dr. Marc Carrier- hematologist and senior scientist at The Ottawa Hospital, associate professor at the University of Ottawa

Authors: Grégoire Le Gal, MD, PhD, Michael J. Kovacs, MD, Laurent Bertoletti, MD, PhD, Francis Couturaud, MD, PhD, Carole Dennie, MD, Andrew M. Hirsch, MD, Menno V. Huisman, MD, PhD, Frederikus A. Klok, MD, PhD, Noémie Kraaijpoel, MD, PhD, Ranjeeta Mallick, PhD, Amanda Pecarskie, BSc, Elena Pena, MD, Penny Phillips, BSc, Isabelle Pichon, BSc, Tim Ramsay, PhD, Marc Righini, MD, Marc A. Rodger, MD, Pierre-Marie Roy, MD, PhD, Olivier Sanchez, MD, PhD, Jeannot Schmidt, MD, PhD, Sam Schulman, MD, Sudeep Shivakumar, MD, Albert Trinh-Duc, MD, Rachel Verdet, BSc, Ulric Vinsonneau, MD, Philip Wells, MD, Cynthia Wu, MD, Erik Yeo, MD, Marc Carrier, MD

Funding: Heart and Stroke Foundation of Canada and French Ministry of Health Programme Hospitalier de Recherche Clinique. Research at The Ottawa Hospital is possible because of generous donations to The Ottawa Hospital Foundation.

Core resources: Ottawa Methods Centre

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