O- Blood Type
O- is the universal donor — compatible with all 8 blood types, making it the most requested type for emergencies.
How common is O-?
O- is one of the less common blood types. Rh-negative types are a minority everywhere, and are notably less common in Middle Eastern populations than in populations of European descent — which is part of why O- donors are in such high demand: this type is both scarce and the universal donor.
Can I donate if I'm O-?
Eligibility to donate blood doesn't depend on your ABO or Rh group — the same general rules apply to every blood type: donors are typically 17–65 years old, weigh at least 50 kg, are in good general health, and wait at least 8 weeks (56 days) between whole-blood donations. What does depend on your type is how much your donation is needed: as the universal donor, your O- blood can go to any of the 8 blood types — it's one of the most requested types for emergencies, when there's no time to test a patient's exact type.
O- and pregnancy
If you are Rh-negative (like O-) and pregnant with an Rh-positive baby, your body can develop antibodies against the baby’s blood type. This is routinely screened for at the first antenatal visit and managed with an Rh immunoglobulin (RhoGAM) injection — it is not a reason to avoid pregnancy, just a reason to get tested early.
Compatibility shown here is for red blood cell donation, the most common type of blood donation. Always confirm eligibility with clinical staff at the donation site. Read the full blood donation guide for eligibility and donation intervals.