What are "rare" blood types?Īlthough ABO and Rh groups are the most important blood groups for transfusions, there are hundreds of other antigens that have been found on the surface of people's red blood cells. In particular, type O-negative blood is in high demand because it's the one most often used for emergencies, when there may not be time to determine a patient's blood type. Type O blood is often in short supply in hospitals, due to demand for this universal donor type, according to the Red Cross. People with type O blood are called "universal donors" because this type can be used for patients with any blood type. (Image credit: Getty Images / mailsonpignata / 500px)
"Universal donars" are people with type O blood, and this blood type can be incredibly useful during medical emergencies. A person's blood type is designated as "positive" if they have the Rh protein on their red blood cells, and "negative" if they don't have this protein. Individuals with type AB blood have both people with type O blood have neither.Īnother protein, the " Rh factor" - also known as the "Rhesus" system - is also present or absent on red blood cells.
Two of the main antigens used for blood typing are known as "A antigen" and "B antigen." People with type A blood only have A antigens on their red blood cells and those with type B blood have only B antigens. A person's blood type is based on whether or not they have certain molecules or proteins - called antigens - on the surface of their red blood cells, according to the National Institutes of Health.