(CNN) - The American Red Cross is asking more blood donors to step up.
The organization said blood donations are at the lowest level in 15 years.
Red Cross officials said all blood types are needed, especially O-negative, O-positive, A-negative and B-negative.
Officials tell USA Today summer is typically a slow time of year, but this year's extreme heat may be keeping donors away.
Copyright 2012 CNN. All rights reserved.