(CNN) - As hundreds lined up to donate blood in the aftermath of the mass shooting at a Pittsburgh synagogue, a new study said that calls for blood donations after such mass-casualty events are not always necessary and may not be the best immediate response to such tragedies.
The study strikes a "delicate balance" and is not meant to dissuade people from donating blood, but it does raise critical questions about how blood donations are used after mass shootings, said Dr. James Lozada, lead author of the study, published Monday in The Journal of Trauma and Acute Care Surgery.
"It's important to convey the message that blood donation is extremely important, but it's important to do it regularly throughout the year," said Lozada, an assistant professor of anesthesiology at Vanderbilt University Medical Center. "The blood that is donated afterwards is very unlikely to be used for these individual tragedies."
Most blood that is donated after these events will be used, he said, but "some of it risks being outdated and going unused."
"Blood is a precious commodity, and we want to use every drop of it," he said. "That's why we encourage people to donate regularly rather than in the immediate aftermaths of these events."
Lozada's study looked at blood donations after the October 2017 shootings in Las Vegas that left 58 people dead and more than 800 wounded. Three Las Vegas health care systems provided data for the study on 220 victims who required hospital admission, including 68 in critical condition.
United Blood Services, the Las Vegas blood bank now called Vitalant, reported receiving 791 donations immediately after the shooting and reported to the study authors that 137 of these donations -- or 17% -- were "wasted," meaning the donated blood went unused and was subsequently discarded, according to the study.
"The public call for blood donors was not necessary to meet immediate demand and led to resource waste," the study concluded. "Preparation for future mass shooting incidents should include training the community in hemorrhage control, encouraging routine blood donation, and avoiding public calls for blood donation unless approved by local blood suppliers."
The American Red Cross, which supplies about 40% of the nation's blood and blood components, said it "is grateful that blood donation is one way people consider helping when tragedy strikes. However, it is important to emphasize that the need for blood is constant and the Red Cross depends on the generosity of volunteer blood donors to provide lifesaving blood for those in need each and every day -- not only during times of emergency."
Arthur Markman, a psychology professor at the University of Texas at Austin who was not affiliated with the study, said it is perfectly natural to want to help out when a tragedy "completely beyond your control" strikes -- whether it be donating money, clothes or blood.
"One of the things we have to do is recognize that we like to be helpful, and we are when we see an event that's out of our control," said Markman, who is also the director of a program called Human Dimensions of Organizations. "It's a tear in the fabric of your life story. Something has happened that is really unexpected."
For those who want to donate blood, Markman recommended scheduling an appointment for later, making it less likely that the blood would go unused.
"There's going to be a need for blood this week and the week after, so take advantage of the impetus to act by scheduling a blood donation for a month from now," he said. "We know if you make a specific plan to the point of putting it on your calendar that you're much more likely to follow through."
Lozada explained why a donation immediately after a mass shooting may not go to the intended victims: "When we go to donate blood, it takes at least two days to process that blood and get it ready to use it for transfusions. But the victims in the event use almost all of their needs within 24 hours. That means the blood you're donating today for a mass shooting is very unlikely to be used for the victims of that tragedy."
As for whether the study findings might come across as deflating for those who desperately want to help, Lozada said, "it's important to convey the message that blood donation is extremely important, but it's important to do it regularly throughout the year."
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