How does COVID-19 affect the blood?

Some people with COVID-19 develop abnormal blood clots, including in the smallest blood vessels. The clots may also form in multiple places in the body, including in the lungs. This unusual clotting may cause different complications, including organ damage, heart attack and stroke.

Researchers think the clotting may be triggered by the high levels of inflammation caused by the SARS-CoV-2 infection. A high level of inflammation can affect multiple organs and result in severe disease.  In children and teens, this high inflammation is called multisystem inflammatory syndrome (MIS-C), and it can particularly affect the heart.

COVID-19 is a disease caused by a virus called SARS-CoV-2. Some people with COVID-19 develop abnormal blood clots, including lots of tiny clots in the smallest blood vessels.

What health conditions may impact how COVID-19 affects my blood?

People who already have damage to the blood vessels from diabetes or high blood pressure may be at higher risk of developing blood clots. In addition, some chronic health conditions may impact how COVID-19 affects your body, including your blood vessels. These include:

Check CDC’s page on higher risk groups for more information on existing medical conditions and COVID-19.

What is the NHLBI doing to support research on how COVID-19 affects the blood?

NHLBI-funded research has helped us understand how inflammation and infection affect the blood.


The NHLBI  also supports new research, including clinical trials that are focused on developing treatments for people infected with SARS-CoV-2.

What can I do to keep myself and others safe?

COVID-19 Clinical Trials 

This searchable database shows federally and privately supported clinical trials studying COVID-19 in the United States and around the world.

Join a RECOVER Clinical Trial

RECOVER is a research project that aims to learn about the long-term health effects of COVID. They need to learn how COVID affects all people, including adults, pregnant people, and children.You can participate whether you have COVID now, had COVID before, or never had COVID.

Getting a COVID-19 vaccine can protect you from COVID-19. Wearing a mask indoors, washing your hands often, and staying at least 6 feet from other people can also help protect you and prevent possibly spreading the virus to others. The CDC provides up-to-date information on how to protect yourself and others.

In addition, consider:

Be sure to check these additional COVID-19 information sources from the U.S. Department of Health and Human Services: