two technicians looking at a vial of blood
two technicians looking at a vial of blood
two technicians looking at a vial of blood

What Does COVID Do to Your Blood?

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Reviewed March 3, 2022

COVID-19 is a very complex illness. The coronavirus that causes COVID-19 attacks the body in many different ways, ranging from mild to life threatening. Different organs and tissues of the body can be affected, including the blood.

Robert Brodsky, a blood specialist who directs the Division of Hematology, and Panagis Galiatsatos, a specialist in lung diseases and critical care medicine, talk about blood problems linked to SARS-CoV-2 — the coronavirus that causes COVID-19 — and what you should know.

Coronavirus Blood Clots

Blood clots can cause problems ranging from mild to life threatening. If a clot blocks blood flow in a vein or artery, the tissue normally nourished by that blood vessel can be deprived of oxygen, and cells in that area can die.

Some people infected with SARS-CoV-2 develop abnormal blood clotting. “In some people with COVID-19, we’re seeing a massive inflammatory response, the cytokine storm that raises clotting factors in the blood,” says Galiatsatos, who treats patients with COVID-19.

“We are seeing more blood clots in the lungs (pulmonary embolism), legs (deep vein thrombosis) and elsewhere,” he says.

Brodsky notes that other serious illnesses, especially ones that cause inflammation, are associated with blood clots. Research is still exploring if the blood clots seen in severe cases of COVID-19 are unique in some way. 

The Impact of Coronavirus Blood Clots Throughout the Body

In addition to the lungs, blood clots, including those associated with COVID-19, can also harm:

The nervous system. Blood clots in the arteries leading to the brain can cause a stroke. Some previously young, healthy people who have developed COVID-19 have suffered strokes, possibly due to abnormal blood clotting.

The kidneys. Clogging of blood vessels in the kidney with blood clots can lead to kidney failure. It can also complicate dialysis if the clots clog the filter of the machine designed to remove impurities in the blood.

Peripheral blood vessels and “COVID toe.” Small blood clots can become lodged in tiny blood vessels. When this happens close to the skin, it can result in a rash. Some people who test positive for COVID-19 develop tiny blood clots that cause reddish or purple areas on the toes, which can itch or be painful. Sometimes called COVID toe, the rash resembles frostbite.

COVID-19, Blood and Immunity: A Pathway to Treatment?

Brodsky’s research is studying the intense inflammation that occurs in some patients who have the coronavirus, and the research may be homing in on a way to prevent the devastating organ damage that COVID-19 causes in some people.

Brodsky and his team have found that the spike protein on the coronavirus activates a part of the immune system known as complement, and hijacks the body’s immune system and turns it against healthy tissue. His group has shown that blocking the complement protein factor D could interrupt the cascade of events that lead to severe illness and organ damage.

“What we discovered is how this coronavirus activates a series of reactions in the immune system that lead to inflammation and cell destruction,” Brodsky says. “Blocking this pathway can prevent that damage.”

Other diseases affect the body using a similar pathway. Brodsky and his research team hope that medicines now in development to treat those conditions might help people with COVID-19.

What about coronavirus and people with sickle cell disease?

“COVID-19 inflammation can lead to dire consequences in people who have blood illnesses, including sickle cell disease,” Galiatsatos says.

Sickle cell disease (SCD) is an inherited blood disorder. According to the U.S. Centers for Disease Control and Prevention, it affects one in about 365 Black Americans. It impacts the shape of red blood cells, which causes pain, organ damage and problems with blood flow. SCD also increases the risk for pneumonia and lung disease.

People with sickle cell disease, even those who are relatively young, seem to be at a high risk for severe COVID-19 and poor outcomes, including death. Since SCD mostly affects Black people, the higher rate of serious coronavirus infections could also be related to longstanding health disparities that leave African Americans more vulnerable to severe illness from the coronavirus. More research will reveal the relationship between sickle cell disease and COVID-19.

Can the coronavirus be spread through blood? Can mosquitoes transmit the coronavirus?

No — donating or receiving blood from a donor is not a risk factor for becoming infected with SARS-CoV-2. Likewise, there is no evidence that anyone has ever caught the virus from a mosquito bite.

Most people get sick from the coronavirus by inhaling droplets or virus particles from an infected person, especially in an enclosed area. If a person touches a surface with active coronavirus on it, and then touches their face and gets the virus in their nose, eyes or mouth, the person can become infected that way, but this is not as common.

Can you donate blood if you’ve had the coronavirus?

Yes. Once you are completely better and your doctor says it is OK, you can safely donate blood. A part of your blood called plasma might even be useful to help other patients. If you have successfully recovered from COVID-19, your blood plasma may contain antibodies to the coronavirus that can be used to help another person fight off the virus.

Do some blood types mean a higher coronavirus risk?

Maybe, but if there are factors in blood type that make people more vulnerable or less vulnerable to COVID-19, the effects might not raise or lower the risk by much.

“There are retrospective studies [comparisons of groups of people with COVID-19 and groups of people without it] that show a possible correlation between blood types O and B and a lower risk of catching SARS-CoV-2 or having a severe case of COVID-19,” Galiatsatos says. “Some of those studies show a pattern of more severe infection among people with type A or AB blood.”

“But these observations result in questions, not answers,” Galiatsatos says, explaining that the research data does not mean a particular blood type is causing severe disease or making people more vulnerable or less vulnerable to the virus.

Brodsky says even if it turns out that different blood type can affect COVID-19 risk, the factor is likely to be very slight. For now, scientists advise not to assume anyone is at a lower or higher risk from the coronavirus due to their blood type.

This article was reviewed by Michael Streiff, M.D., medical director of the Johns Hopkins Special Coagulation Laboratory.

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