What are the blood types?
There are 8 main blood types: A+, A-, B+, B-, AB+, AB-, O+ and O-. They come from the ABO system (A and B antigens) combined with the Rh factor (positive or negative).
Blood types are classified mainly by two systems: ABO and Rh. Together they give eight types.
| Type | ABO antigens | Rh | Approximate share of US population |
|---|---|---|---|
| O+ | None | Positive | 37% |
| A+ | A | Positive | 36% |
| B+ | B | Positive | 8% |
| O- | None | Negative | 7% |
| A- | A | Negative | 6% |
| AB+ | A and B | Positive | 3% |
| B- | B | Negative | 2% |
| AB- | A and B | Negative | 1% |
Figures are approximate and differ by ethnic background and source.
ABO system
- Type A: A antigen and anti-B antibodies
- Type B: B antigen and anti-A antibodies
- Type AB: both antigens, no antibodies
- Type O: no A or B antigen
Rh factor
If you have the D antigen you are Rh positive. If you do not, you are Rh negative and should not receive Rh positive red cells without evaluation.
Who can donate red cells to whom
| Donor | Can give to |
|---|---|
| O- | All types |
| O+ | O+, A+, B+, AB+ |
| A- | A-, A+, AB-, AB+ |
| A+ | A+, AB+ |
| B- | B-, B+, AB-, AB+ |
| B+ | B+, AB+ |
| AB- | AB-, AB+ |
| AB+ | AB+ |
Why O- is special
O negative red cells can be given to almost anyone, so hospitals rely on them in emergencies when there is no time to test the patient's type.
This information is general and does not replace advice from a health professional. Your eligibility is always decided at the donor screening on the day of donation. Rules change, so confirm with the American Red Cross or the blood center where you plan to donate.