University of Iowa Health Science Relations and
Mitch Overton
Donor Recruitment Coordinator
First Published: 2000
Last Revised: October 2004
Peer Review Status: Internally Peer Reviewed

Before 1900, blood transfusions were dangerous because nobody knew that there are several different "types" of blood.

About 1900 four types of blood were distinguished and called types 0, A, B, and AB. In 1939, the RH factor was discovered. Since the RH factor could be either positive (RH+) or negative (RH-), the number of blood types was expanded to eight.

Do you know what your blood type is?

"Whichever type of blood you have, your blood is needed to help someone," says Mitch Overton, director of donor recruitment for the University of Iowa's DeGowin Blood Center. "Accident victims and patients undergoing major surgery such as open heart operations may need several pints of blood."

Although other factors may be used for classification in special cases, the basic blood groups are found in the population in these percentages:

• 0 RH+, 38 percent
• 0 RH-, about 7 percent
• A RH+, 35 percent
• A RH-, 6 percent
• B RH+, 8.5 percent
• B RH-, 1.5 percent
• AB RH+, 3.4 percent
• AB RH-, less than 1 percent.

To find out more about donating blood, contact your community hospital or your regional blood bank. Donation information for Eastern Iowans is available from the DeGowin Blood Center.