The claim: An image shows the blood of a vaccinated person is darker than the blood of an unvaccinated person
A photo published Sept. 17 on Instagram shows a screenshot of a message thread. The first message includes an image of what appears to be two bags of blood. The bag on the right is a darker shade of red, and a message below the image reads: "Left vs. Right= non vax vs. Vax."
"Looks like a bag of blood clots," reads the post's caption. "Nothing to see. Totally normal."
The post accumulated more than 4,500 likes within a week. But an expert told USA TODAY the vaccines do not affect the color of blood.
USA TODAY reached out to the Instagram user who shared the claim for comment.
Vaccination doesn't affect blood color
There is no substance to the claim that COVID-19 vaccines change the color of blood, according to Dr. Pampee Young, chief medical officer of biomedical services at the American Red Cross.
"At the American Red Cross, we visually inspect all donated units and have not seen that COVID-19 vaccinated blood units change the color of blood," she said in an email exchange with USA TODAY.
Red blood cells contain a molecule called hemoglobin, which transports oxygen through the body and gives the cells their red color, according to Medical News Today. The level of oxygen in blood cells determines the shade of red.
When blood leaves the heart it is oxygen-rich and has a bright red color. Blood that is returning to the heart has less oxygen, resulting in a darker color.
Young said the hue of blood can vary naturally due to a number of factors. This includes minor variations in individual levels of chemical compounds carried by plasma, or variations in oxygen, iron, lipids and red blood cells.
"It’s important to note that donating blood after receiving a COVID-19 vaccine does not reduce a donor’s protection from the virus," she said.
Research has indicated the coronavirus vaccines are associated with a slightly higher risk of blood clots. But those side effects are rare – and the risk is much higher for COVID-19 itself.
Our rating: False
Based on our research, we rate FALSE the claim that an image shows the blood of a vaccinated person is darker than the blood of an unvaccinated person. Vaccination has no effect on the color of blood, which is primarily determined by the level of oxygen in blood cells.
Our fact-check sources:
USA TODAY, April 12, Fact check: No evidence of miscarriage surge since vaccine rollout
USA TODAY, April 30, Fact check: COVID-19 vaccines don’t cause death, won’t decimate world’s population
USA TODAY, Dec. 14, 2020, Fact check: A false post on social media claims COVID-19 vaccine causes infertility in women
Medical News Today, April 10, 2018, Is blood actually blue?
AP, Sept. 20, COVID-19 vaccines do not change color of blood
Dr. Pampee Young, Sept. 24, Email exchange with USA TODAY
Medical News Today, June 30, 2017, Why is blood red?
The New York Times, Aug. 27, A study confirms a small risk of blood clots after vaccines, but not as high as the risk Covid brings.
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This article originally appeared on USA TODAY: Fact check: COVID-19 vaccines don't change blood color