The American Red Cross has experienced a shortfall equivalent to not receiving donations for four days. View Full Caption Shutterstock

CHICAGO — The American Red Cross has issued another emergency call for blood and platelet donors as it continues to face a critical blood shortage.

An emergency call was issued earlier this month, which resulted in a 30 percent increase in donations. Despite the increase, the Red Cross saw 61,000 fewer donations in May and June, which is the equivalent to not receiving any donations at all for more than four days.

The American Red Cross is urging eligible donors of all blood types to donate immediately. As a thank you, the Red Cross will be emailing those who donate a $5 Target eGiftCard through August 31.

"We sincerely appreciate those who have responded to the call to help save lives and encourage those who haven't to consider rolling up and give the gift of life. It only takes an hour but it can mean a lifetime for patients," Red Cross Blood spokesman Nick Gehrig said.

The blood shortages are happening all over the country and are common during the summer due to traveling and vacations, says Laura McGuire, external communications manager at Red Cross.

About 20 percent of the blood supply for the Red Cross comes from high schools and colleges, says McGuire, another factor that contributes to the decline during the summer.

The Red Cross is in need of all blood types and has a "sweet spot" for two types in particular: O negative blood and AB plasma which are both universal, allowing trauma and emergency rooms to respond more quickly when they patient's blood type is unknown.

Several upcoming blood donation opportunities are scheduled through August 24.

Here is where and when you can donate:

• 8:30 a.m.-1:30 p.m. July 26 at Bank of America, 135 S. LaSalle St.

• 10 a.m.-3 p.m. July 27 at Doubletree, 300 E. Ohio St.

• 9 a.m.-2 p.m. Aug. 1 at 300 N. LaSalle St.

• 9 a.m.-2 p.m. Aug. 3 at One North Franklin, 1 N. Franklin St.

• 9 a.m.-3 p.m. Aug. 14 at Willis Tower, 233 S. Wacker Dr., Franklin side

• 12:30-5:30 p.m. Aug. 21 at the InterContinental Hotel, 505 N. Michigan Ave.

• 9 a.m.-2 p.m. Aug. 22 at Marc Realty, 55 E. Jackson Blvd., Office of the Building

• 3 p.m.-7 p.m. Aug. 22 at DePaul University Ray Meyer Fitness and Recreation Center, 2235 N. Sheffield Ave.

• 3 p.m.-7 p.m. Aug. 23 at DePaul University Ray Meyer Fitness and Recreation Center, 2235 N. Sheffield Ave.

• 9 a.m.-2 p.m. Aug. 24 at 120 S. LaSalle St.