Clots In COVID-19 Tied To Illness Severity, Not Virus Itself

COVID-19 does not independently increase the risk of pulmonary embolism (PE), new findings suggest.

"We believe that while some patients with COVID-19 clearly do have a pro-thrombotic state, with potential for developing blood clots in many parts of their bodies, the overall group of patients with COVID-19 are not at substantially higher risk than patients who come to the hospital for other diseases," Dr. Mark M. Hammer of Harvard Medical School told Reuters Health by email.

While a number of studies have reported a high incidence of PE in COVID-19 patients, all severely ill patients are at increased risk of thromboembolism, and many of these studies didn't include a control group of COVID-19-free patients, Dr. Hammer and his team note in JACC: Cardiovascular Imaging.

Their study included patients who had been tested for SARS-CoV-2 by RT-PCR between March 1 and May 1 and had undergone computed tomography pulmonary angiography (CTPA) within seven days prior to and 14 days after the test.

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The researchers analyzed 696 CTPA scans from 674 patients, a quarter of whom tested positive for COVID-19. There were 170 CTPAs for patients with COVID-19, and 20 (11.8%) were positive for PE, versus 45 of 526 CTPAs (8.6%) from patients without COVID-19 (P=0.14).

Among intubated patients, seven of the 23 patients with COVID-19 had PE (30.4%), versus six of 33 patients without COVID-19 (18.2%, P=0.22).

Average D-dimer level was 2,616 ng/mL for patients with COVID-19 and 2,354 ng/ml for uninfected patients (P=0.12). D-dimer was the only variable independently associated with PE; age, sex, COVID-19 status and intubation were not.

The only significant difference in PE incidence was seen in patients who had a CTPA within a day of their COVID-19 test, 14.1% of whom were positive for PE, versus 7.7% of COVID 19-negative patients (P=0.04). This could have been because the patients with COVID-19 hadn't yet received prophylactic anticoagulation, Dr. Hammer said.

"The phenomenon of high rates of blood clotting is probably not unique to COVID-19. Reports from the prior pandemic of H1N1 influenza also mentioned high rates of blood clotting," he added. "It is likely that these viruses can cause, in some patients, a very strong inflammatory response that leads to blood clotting."

—Anne Harding

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