Your risk of developing a blood clot is high after COVID-19, the study says

By now, most people are aware of the risks of developing long COVID after COVID-19. But new research suggests that the virus may increase the risk of a blood clot developing – and that risk remains higher than normal for a year later.

This is the main finding of a large new study published in the journal Circulation. The study looked at data from 48 million people enrolled in the UK’s national healthcare system from January 2020 to the day before COVID-19 vaccines became available in December 2020. Researchers found 1.4 million COVID-19 diagnoses, including 10,500 patients who have developed problems related to blood clots.

The researchers found that in the first week after receiving the COVID-19 diagnosis, the risk of developing an arterial blood clot (which could lead to a heart attack or stroke by blocking blood flow to the heart or brain) was almost 22 times higher than someone who didn’t have the virus. The risk dropped in the second week but was still elevated – less than four times higher than someone who did not have the virus.

For blood clots that occur in the veins, such as deep vein thrombosis and pulmonary embolism, the risk in the first week after being diagnosed with COVID-19 was 33 times higher. After three to four weeks of being diagnosed, a person was about eight times as tall as that. The risk was still 1.8 times higher between 27-49 weeks later compared to people who had never had COVID-19.

The risk was no matter how severe COVID-19 was, but it was higher in people hospitalized with the virus. The risk of blood clots was also higher in Black and Asian patients.

Overall, clots were rare. The overall risk of developing an arterial clot at 49 weeks after being diagnosed with COVID-19 was 0.5% and 0.25% for a venous clot during this period. (To translate this into real health problems, this led to approximately 7,200 additional heart attacks or strokes, and 3,500 additional cases of pulmonary embolism, deep vein thrombosis, or other vein-related health problems.)

This raises many post-COVID-19 safety questions, including why it happens and what you should be aware of. Here’s what you need to know.

Why might COVID-19 increase the risk of a blood clot?

The study did not investigate this – it just found a link – but there are some theories as to why this link might exist.

The big thing is that the virus can cause inflammation in your body. “COVID causes an inflammatory response that can increase blood clotting and damage vascular structures,” said infectious disease expert Dr. Amesh A. Adalja, senior research fellow at the Johns Hopkins Center for Health Security. As a result, he says, “the increased risk of clotting may persist.”

It’s also possible that the increased risk of blood clots is simply how the virus works, says Dr. Thomas Russo, professor and head of infectious disease at the University of Buffalo in New York. “It seems to be part of the pathophysiology of this virus,” he says.

Dr. Russo says doctors knew “from the start of this pandemic that when you catch COVID” you are more likely to form blood clots. “At first, we saw these awful situations of people with black fingers and toes and damage to various organs,” due to blood clots, he says.

Could this happen with other infections?

Doctors say that other infections may put you at a higher than usual risk of developing a blood clot. Dr. Adalja points out that the compound is “well described” in herpes zoster, which increases the risk of a heart attack.

“These clots have also been described as the flu,” says Dr. Russo. “However, they’re more common with COVID.”

Signs of a blood clot

Blood clotting is normal under certain circumstances, for example if you cut yourself. However, according to Medline Plus, blood clots can be a problem when they form and form a blockage or travel to other areas of the body, such as the lungs or the brain. Symptoms of dangerous clots depend on their location in the body. On Medline Plus, these may include:

  • Abdominal pain
  • Nausea
  • Vomiting
  • Sudden or gradual pain in your arm along with swelling, tenderness and warmth
  • Dyspnoea
  • Pain with deep breathing
  • Rapid breathing
  • Increased heart rate
  • Speech problems
  • Sight problems
  • Seizures
  • Weakness on one side of the body
  • Sudden, severe headache
  • Pain in the chest
  • Exploitation
  • Dyspnoea
  • Pain in the left arm

How to stay safe from blood clots if you have COVID-19?

Dr. Adalja emphasizes that this risk is rare. However, Dr. Russo says it’s still good to at least be aware of the risk of a blood clot forming and what the symptoms may look like.

Dr. Russo says it’s also a good idea to get the full COVID-19 immunization series, including the booster doses you’re eligible for, whether you’ve had COVID or not. “This is another reason to try to protect yourself from COVID,” he says.

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