CHICAGO (CBS) — Blood banks across the city are feeling the impact of the nation’s dangerously low blood supply – and after a violent holiday weekend, Chicago’s demand for blood donations swelled even higher.

As CBS 2 Investigator Megan Hickey reported Thursday, we have not yet heard about hospitals having to cancel surgeries. But hospitals such as Northwestern Memorial Hospital are changing their transfusion procedures to conserve as much blood as possible – and are urging more people to donate.

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Dr. Glenn Ramsey is the medical director of Northwestern’s blood bank – a position he has held for three decades.

“This is probably as low as its been maybe in the past 10 years or so,” he said.

Many blood centers nationwide have less than a one-day supply on hand.

“We’ve probably been down to as low as maybe 55 or 60 percent of our normal inventory,” Ramsey said.

Dr. Ramsey said Northwestern Memorial has seen a 15 percent increase in demand. They’re having to conserve.

“We’re also encouraging physicians to give only one unit at a time, and then evaluate their patients before they get a second unit automatically,” he said.

And with shooting victims in the triple digits after the long Fourth of July weekend, blood supplies at level one trauma centers were even more valuable.

“We had a lot of penetrating trauma – mostly gunshot wounds – and those are patients who tend to need blood,” said Dr. Geoffrey Wool, blood bank medical director at UChicago Medicine.

Wool said UChicago Medicine was able to acquire extra blood this weekend. But lately, their scheduled orders for critical red cell types have been cut in half.

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There is a shortage in particular of Type O, the universal donor.

“It tends to be the blood type that’s most in demand and in shortest supply, and that was what was being hit the most was the group O supply that we get out of our blood suppliers,” Wool said.

So how did we get here? Dr. Ramsey and Dr. Wool said there are a lot of factors.

Patients that may have pushed off medical treatment during the height of the pandemic are now coming in for surgeries. Combine that with schools, businesses, and churches being unable to hold many large blood drives.

“If we don’t get the blood supply back or if the blood supply keeps going down from where it is now, we might have to start thinking about the (operating room) schedule,” Ramsey said.

But Dr. Wool said canceling surgeries isn’t necessarily a fix.

“It’s the traumas; it’s the unexpected bleeding that ends up being a large portion of the demand on our blood bank,” Wool said, “and those, you can’t really schedule.”

Hospital systems say there is a significant need to grow the blood donor base and create long-term, committed donors. If it gets worse, canceling surgeries could be the next step.

For information on how to donate, follow the links below.

Red Cross

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You can also donate blood to the University of Chicago Medicine Blood Donation Center. Appointments there can be scheduled by calling (773) 702-6247.

Megan Hickey