Craig Coopersmith was up early that morning as usual and typed his daily inquiry into his phone. “Good morning, Team Covid,” he wrote, asking for updates from the ICU team leaders working across 10 hospitals in the Emory University health system in Atlanta.

One doctor replied that one of his patients had a strange blood problem. Despite being put on anticoagulants, the patient was still developing clots. A second said she’d seen something similar. And a third. Soon, every person on the text chat had reported the same thing.

“That’s when we knew we had a huge problem,” said Coopersmith, a critical-care surgeon. As he checked with his counterparts at other medical centers, he became increasingly alarmed: “It was in as many as 20, 30 or 40% of their patients.”

One month ago, when the country went into lockdown to prepare for the first wave of coronavirus cases, many doctors felt confident they knew what they were dealing with. Based on early reports, the novel coronavirus appeared to be a standard variety respiratory virus, albeit a contagious and lethal one with no vaccine and no treatment. They’ve since seen how COVID-19, the disease the novel coronavirus causes, attacks not only the lungs but the kidneys, heart, intestines, liver and brain.

Increasingly, doctors are reporting bizarre, unsettling cases that don’t seem to follow any of the textbooks they’ve trained on. They describe patients with startlingly low oxygen levels — so low that they would normally be unconscious or near death — talking and swiping on their phones. Asymptomatic pregnant women suddenly in cardiac arrest. Patients who by all conventional measures seem to have mild disease deteriorating within minutes and dying at home.

With no clear patterns in terms of age or chronic conditions, some scientists hypothesize that at least some of these abnormalities may be explained by severe changes in patients’ blood.

The concern is so acute some doctor groups have raised the controversial possibility of giving preventive blood thinners to everyone with COVID-19 — even those well enough to endure their illness at home.

Blood clots, in which the red liquid turns gel-like, appear to be the opposite of what occurs in Ebola, Dengue, Lassa and other hemorrhagic fevers that lead to uncontrolled bleeding. But they actually are part of the same phenomenon — and can have similarly devastating consequences.

Autopsies have shown some people’s lungs filled with hundreds of microclots. Errant blood clots of a larger size can break and travel to the brain or heart, causing a stroke or heart attack. On Saturday, Broadway actor Nick Cordero, 41, had his right leg amputated after being infected with the novel coronavirus and suffering from clots that blocked blood from getting to his toes.

Phenomenon different

Lewis Kaplan, a University of Pennsylvania physician and head of the Society of Critical Care Medicine, said that every year doctors treat people with clotting complications, from those with cancer to victims of severe trauma, “and they don’t clot like this.”

“The problem we are having is that while we understand that there is a clot, we don’t yet understand why there is a clot,” Kaplan said. “We don’t know. And therefore, we are scared.”

The first sign something was going haywire was in legs, which were turning blue and swelling. Even patients on blood thinners in the ICU were developing clots — which is not unusual in one or two patients in one unit but is unusual for so many at the same time. Next came the clogging of the dialysis machines, which filter impurities in blood when kidneys are failing and jammed several times a day.

“There was a universal understanding that this was different,” Coopersmith said.

Then came the autopsies. When they opened up some deceased patients’ lungs, they expected to find evidence of pneumonia and damage to the tiny air sacs that exchange oxygen and carbon dioxide between the lungs and the bloodstream. Instead, they found tiny clots all over.

Video meetings were convened in some of the largest medical centers nationwide. Tufts. Yale-New Haven. The University of Pennsylvania. Brigham and Women’s. Columbia-Presbyterian. Theories were shared. Treatments debated.

Although there was no consensus on the biology of why this was happening and what could be done about it, many came to believe the clots might be responsible for a significant share of U.S. deaths from COVID-19 — possibly explaining why so many people are dying at home.

Early signs

In hindsight, there were hints blood problems had been an issue in China and Italy as well, but it was more of a footnote in studies and on information-sharing calls that had focused on the disease’s destruction of the lungs.

“It crept up on us. We weren’t hearing a tremendous amount about this internationally,” said Greg Piazza, a cardiovascular specialist at Brigham and Women’s who has begun a study of bleeding complications of COVID-19.

Helen Boucher, an infectious-disease specialist at Tufts Medical Center, said there’s no reason to think anything is different about the virus in the United States. More likely, she said, the problem was more obvious to American doctors because of the unique demographics of U.S. patients.