Blood donations at University Hospital spiked during Hurricane Harvey. August was on track to be a good month hovering around 300 donors. The hurricane doubled that number to 612.

The pattern of tragedy equaling a surge in blood donation was evident in Las Vegas following the mass shooting that killed 59 and injured another 527. Lines of donors flocked to provide aid by giving blood.

"The most important thing about the blood supply is like a pipeline. It's not a bank," Dr. Leslie Greebon said.

Dr. Greebon is the director of the blood lab at University Hospital. The hospital has its own blood donation center. She says that donations are welcome but wishes the donations were more continuous rather than all at once.

"We need that blood beforehand," she said. "If you donate today, it may not be ready for three to four days from now."

Blood can't be given to a patient in need the day of the donation. There's a process which takes a few days. Dr. Greebon noted that red blood cells can be stored for 42 days and platelets can be held for five days. During huge donation periods associated with tragedies and disasters, centers will schedule donors to come back at a later time to keep the supply continuous.

Blood donated in San Antonio could help victims in other states, depending on need at other hospitals in their network that regional blood centers have set up.

University Hospital's donation center is open Monday through Friday.