Blood banks are struggling trying to stock up as the nation deals with a low number of donors.

"It's the easiest way to help someone else," Rio Grande Valley blood donor Tom Shanahan said.

That's why Shanahan donates blood and why he hopes others will, too. Especially now, when it's needed the most.

The American Red Cross declared a nationwide blood shortage-emergency this week. They've seen the lowest number of donors in 20 years.

Rio Grande Valley blood banks say fewer donors are also coming through their doors.

"You see like a maybe a 10 to 15 percent drop because of travel, illnesses," Vitalant Donor Recruitment Manager Ali Arredondo said.

There's a drop in donors every year during the holiday season, but the lack of donors doesn't leave much room for backup.

Arredondo says right now they have a 14-day blood supply, but two weeks is based on a "normal" need. 

If a mass emergency or natural disaster happened in the Valley, there's a chance those reserves would not be enough.

"If there's a trauma situation, or there's an accident, a patient can use up to 90 pints of blood. That's 90 donations," Arredondo said.

He says there are misconceptions about who can donate.

Having diabetes is one reason people are worried about donating, but health experts say you're still eligible.

Anyone willing to donate at Vitalant can call ahead for an appointment or walk-in.

Watch the video above for the full story.