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COVID-19 Thickens Blood, Causes Strokes In Some Patients With Mild Symptoms


Now the emerging link between COVID-19 and life-threatening blood clots. As NPR's Jon Hamilton reports, the disease appears to thicken the blood, which can lead to clots that affect the lungs and kidney and to strokes that damage the brain.

JON HAMILTON, BYLINE: When the coronavirus arrived in New York, hospital emergency rooms began to see some unusual stroke patients. Dr. J. Mocco directs the Cerebrovascular Center at Mount Sinai.

J MOCCO: We had a young woman in her early 30s who came in with a profound stroke, the kind of stroke that leaves someone permanently paralyzed and possibly unable to survive.

HAMILTON: A stroke caused by a clot. The young woman had none of the usual risk factors for stroke, but she tested positive for the virus that causes COVID-19, so Mocco and other doctors began to compare notes.

MOCCO: Speaking with the ICU doctors and the pulmonary doctors, they were seeing clots in the lungs. Speaking with the renal doctors and the dialysis doctors, they were seeing clots in the renal arteries causing kidney injury.

HAMILTON: Mocco and a group of doctors thought it was time to sound the alarm, so they described five stroke patients in a letter that appears today in The New England Journal of Medicine.

MOCCO: These were five patients in their 30s and 40s who did not have the typical risk-factor profile but did have the SARS-CoV-2 virus.

HAMILTON: The letter supports something other doctors have observed since the pandemic began in China. COVID-19 seems to produce blood clots - a lot of them. Dr. Craig Coopersmith is the interim director of the Critical Care Center at Emory University in Atlanta.

CRAIG COOPERSMITH: Patients who are in the intensive care unit for other diseases are at risk of having clots but nothing like the levels that we're seeing in COVID-19.

HAMILTON: Coopersmith says he hasn't seen the sort of stroke patients reported in New York - young people without risk factors. But he says clotting problems are affecting a significant minority of patients in the ICU. And that includes people on dialysis, which he finds surprising.

COOPERSMITH: Patients on dialysis in the intensive care unit with COVID - patients on that are on blood thinners, and the dialysis machines almost never clot. And we were finding that the machines were clotting two or three or four times a day.

HAMILTON: Blood thinners do reduce clotting, and other drugs can often dissolve a clot before it causes major damage. But Coopersmith says all of these drugs can cause bleeding, so patients have to be watched closely.

COOPERSMITH: We have literally five different teams in the hospital specifically and only looking at blood clotting just because of this just in COVID.

HAMILTON: It's still not clear precisely how COVID-19 is causing blood clots. It could be from the infection itself or the immune system's response to the virus. But Dr. Tiffany Osborn of Washington University in St. Louis says doctors are beginning to figure out what's happening.

TIFFANY OSBORN: What we're seeing that contributes to our understanding of that are lab values that are off the wall.

HAMILTON: For example, doctors are seeing crazy high levels of a protein fragment called D-dimer. This suggests that the body is trying to break down clots. Patients also have high levels of thrombin, which is involved in clot formation. And Osborn says the evidence that COVID-19 is causing clots in lots of places would explain an odd symptom that she and other doctors have seen.

OSBORN: You have areas that start to become purple on the hands and on the feet. We think it probably has to do with these blood clots that are going to the extremities.

HAMILTON: Doctors are still relying on anecdotal evidence to treat clots in COVID patients, but Osborn says that's better than no evidence at all.

Jon Hamilton, NPR News.

(SOUNDBITE OF MUSIC) Transcript provided by NPR, Copyright NPR.

Jon Hamilton is a correspondent for NPR's Science Desk. Currently he focuses on neuroscience and health risks.