Often abbreviated ABO, blood types are inherited and fall into four groups or types: O, A, B, AB. Each blood type also is identified as either Rh positive or negative (the Rh factor being an inherited blood group on red blood cells). Approximately 85% of the U.S. population is Rh-positive (i.e., O+, A+, B+, AB+). Those who do not have the Rh factor are Rh-negative (O-, A-, B-, AB-) and are quite rare.
|O-||7%||Universal red cell donors|
|AB+||3%||Universal plasma donors and red cell recipients|
|AB-||1%||Universal plasma donors|