Conference Coverage

COVID-19 and Blood Clots: Inside the Battle to Save Patients

Protocols are now in place to prevent thrombosis, hematologist-oncologist tells colleagues at AVAHO Virtual Meeting.


Abnormal coagulation is a hallmark of COVID-19. Now, as we’re learning more about the high risk of thrombosis, physicians need to prescribe prophylaxis routinely in the hospital, stay alert, and act immediately when signs of trouble appear. “We must have a low suspicion for diagnosis and treatment of thrombosis,” said hematologist-oncologist Thomas DeLoughery, MD, professor of medicine at Oregon Health & Science University in Portland in a presentation at the virtual 2020 annual meeting of the Association of VA Hematology/Oncology (AVAHO).

Still, research is sparse, and there are disagreements about the best strategies to protect patients, said DeLoughery. Physicians recognized coagulation problems early on during the course of the COVID-19 pandemic, he said, and they’re very common. According to DeLoughery, most patients have abnormal coagulation, very high D-dimer test results, and very high fibrinogen levels—even to the extraordinary level of 1,500 mg/dL, he said. And unlike in typical patients with septic shock, patients with thrombosis have a higher risk than bleeding.

A high D-dimer level is a major prognostic indicator of thrombosis and bad outcomes. “It’s representative of widespread coagulation activation, and it can be a sign of pulmonary thrombosis and local thrombosis happening at the site of the COVID infection,” he said.

DeLoughery highlighted an April 2020 study that found that “patients with D dimer levels ≥ 2.0 µg/mL had a higher incidence of mortality when compared with those who with D dimer levels < 2.0 µg/mL (12/67 vs 1/267; P < .001; hazard ratio, 51.5; 95% CI, 12.9 206.7).”

Research also suggests that “there's something about getting COVID and going to the intensive care unit (ICU) that dramatically raises the risk of thrombosis,” he said, and the risk goes up over time in the ICU. Venous thrombosis isn’t the only risk. Relatively young patients with COVID have suffered from arterial thrombosis, even though they have minimal to no respiratory symptoms and no cardiovascular risk factors.

As for treatments, DeLoughery noted that thrombosis can occur despite standard prophylaxis, and patients may show resistance to heparin and, therefore, need massive doses. Still, there’s consensus that every patient with COVID-19 in the hospital should get thromboprophylaxis with low-molecular-weight heparin (LMWH), he said, and unfractionated heparin is appropriate for those with renal failure.

“The problem is everything else is controversial,” he said. For example, hematologists are split evenly on whether heparin dosing should be increased beyond standard protocol for patients in the ICU with 1.5 to 3 times normal D-dimers levels. He agreed with this approach but notes that some centers set their D-dimer triggers higher—at 3 to 6 times the normal level.

“The problem is that there’s limited data,” he said. “We have lots of observational studies suggesting benefits from higher doses, but we have no randomized trial data, and the observational studies are not uniform in their recommendations.”

What about outpatient prophylaxis? It appears that risk of thrombosis is < 1% percent when patients are out of the hospital, he said. “This is very reassuring that once the patient gets better, their prothrombotic drive goes away.”


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