A coronavirus patient thought he was recovering. Then doctors found blood clots in his lungs — a new and potentially deadly complication of the virus.

• Doctors are finding blood clots in the lungs, heart, and kidneys of coronavirus patients, some of whom are critically ill and others who seem relatively stable.
• Blood clots can travel and create blockages in veins, which could lead to strokes, heart attacks, and other issues.
• With the absence of clinical trials or science-backed treatments, physicians are being forced to figure out how to best treat these complications on "very weak but very compelling data," Dr. Alex Spyropoulos, an expert on blood clots at Northwell Health in New York told Business Insider.
• Business Insider talked to Michael Reagan, a 49-year-old COVID-19 patient whose doctors recently discovered dozens of blood clots in his lungs.
• Read live updates about the coronavirus here.

More than 2 million people around the world have been infected with the novel coronavirus, but there's still a lot we don't know about how the disease affects the human body.

Respiratory issues are one of the key symptoms of infection, but other complications — like kidney issues and heart problems — have more recently risen to the surface as physicians struggle to better understand how to treat their patients.

With COVID-19, the disease caused by the coronavirus, doctors are also seeing blood clots occurring in the lungs and bodies of patients. Clots can travel and create blockages in veins, leading to strokes, heart attacks, and other issues.

Some of the patients with blood clots are in hospitals in critical condition while others diagnosed with the complications are otherwise healthy enough to be sent home.

That's what happened to Michael Reagan, a 49-year-old COVID-19 patient.

'It feels like a toxin is in my body'

Reagan, who works for an international biomedical company in New York, was diagnosed with COVID-19 in late March and had been recovering at home in New York City for weeks. He was taking azithromycin, an antibiotic used to treat infections, and hydroxychloroquine, an anti-malarial medication, as a participant in a clinical trial.

His symptoms included breathing problems, a high fever, and coughing up blood. Reagan said he was starting to feel a little better early last week, until he suddenly began to experience a high fever once again, along with chest pains.

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When he went into the hospital, Reagan said doctors told him coronavirus-related pneumonia has spread into both lungs. A pulmonologist later told him he had dozens of little blood clots throughout his lungs.

"It feels like a toxin is in my body," Reagan told Business Insider.

Blood clots in recovering coronavirus patients are a new worry for doctors. In early autopsy data from Northwell Health, around 40% of coronavirus patients who died after leaving the hospital appeared to have experienced major clotting events like a massive heart attack or lung clots, as previously reported by Business Insider.

In a recent observational study, Dutch researchers reported that around one-third of the 184 coronavirus patients they observed in the intensive care unit had a complication associated with a clot.

To treat his blood clots, Reagan ended up staying overnight in a hospital to receive tissue plasminogen activator (TPA), a protein used to treat heart attacks and strokes which helps break down blood clots. Reagan was then sent home with Eliquis, a blood thinner.

"I had no idea a blood clot could hurt so bad," Reagan said.

Because the pain is so intense, Reagan said that he has trouble bending over or lifting his left arm.

"I'm just trying to be still and let myself heal," he said

Read more: The US is sprinting to develop a coronavirus vaccine or treatment. Here's how 19 top drugmakers are racing to tackle the pandemic.

Figuring out the best way to treat coronavirus complications

Blood clots can occur in severely ill patients in intensive care units, or even in patients who are hospitalized. While in the ICU, patients are typically on breathing support and sedated, which limits their ability to move as they heal. Staying still raises the risk of clots.

Some doctors think there's something about the coronavirus that leads to more clotting issues, though.

And in the absence of clinical trials or science-backed treatments, doctors are being forced to figure out how to best treat these complications with relatively little guidance, Dr. Alex Spyropoulos, an expert on blood clots at Northwell Health in New York told Business Insider.

Spyropoulos recently told Business Insider that he has been relying on his clinical experience to make decisions to prevent clotting complications in COVID-19 patients.

"If you have a deep experience in this field you can make reasonable assumptions and extrapolations and observations from indirect data," he said.

For the past month, Spyropoulos has been working to step up preventive dosing of blood thinners for COVID-19 patients and ensuring that physicians are aware of signals that might indicate clotting, such as swelling in the legs of patients.

Read more: Experts just set out a playbook for how governors should reopen states, and it includes 2- to 3-week phases with distancing measures applied to places like restaurants and outdoor events

Recovering is a slow journey

Reagan told Business Insider that the coronavirus is unlike any flu or pneumonia he's experienced. He said that whenever he's had those illnesses he's felt better after a few weeks, at least enough to go out and be active.

Reagan was diagnosed with the coronavirus over a month ago. He said he still gets exhausted just by doing small things, like getting dressed or taking a shower.

"It really does feel like I've been poisoned," he said.

Pointing to states like Georgia and Florida, whose governors have recently indicated that they want to ease stay at home orders, Reagan added that he hopes states don't rush to end shelter in place orders anytime soon.

"I really believe it's socially irresponsible to be opening things back up," he said. "It's a deadly virus. It's not a simple flu and it can change your life."

Read more: The US is depending on tests that can tell if you've ever had the coronavirus to help reopen the economy. But millions are flooding the market and we don't know how accurate they really are.

Read the original article on Business Insider