Blood types are determined by the presence or absence of certain antigens – substances that can trigger an immune response if they are foreign to the body. Since some antigens can trigger a patient's immune system to attack the transfused blood, safe blood transfusions depend on careful blood typing and cross-matching. Therefore, there are four major blood groups determined by the presence or absence of two antigens – A and B – on the surface of red blood cells. Moreover, there is a protein called the Rh factor, which can be either present (+) or absent (–), creating the 8 most common blood types (A+, A-, B+, B-, O+, O-, AB+, AB-). There are more than 600 other known antigens, the presence or absence of which creates "rare blood types." Here is everything you need to know about blood types.
So, there are eight possible blood types:
- O negative. This blood type doesn't have A or B markers, and it doesn't have Rh factor.
- O positive. This blood type doesn't have A or B markers, but it does have Rh factor. O positive blood is one of the two most common blood types.
- A negative. This blood type has A marker only.
- A positive. This blood type has A marker and Rh factor, but not B marker. Along with O positive, it's one of the two most common blood types.
- B negative. This blood type has B marker only.
- B positive. This blood type has B marker and Rh factor, but not A marker.
- AB negative. This blood type has A and B markers, but not Rh factor.
- AB positive. This blood type has all three types of markers — A, B, and Rh factor.
Having any of these markers doesn't make a person's blood any healthier or stronger. It's just a genetic difference, like having blue eyes instead of green or straight hair instead of curly.
Antibodies and antigens
Blood is made up of red blood cells, white blood cells and platelets in liquid called plasma. The blood group is identified by antibodies and antigens in the blood. Antibodies are proteins found in plasma. They're part of your body's natural defenses. Of course, they recognize foreign substances, such as germs, and alert your immune system, which destroys them. Antigens are protein molecules found on the surface of red blood cells.
The Rh Factor
Each blood type is also grouped by its Rhesus factor, or Rh factor. Blood is either Rh positive (Rh+) or Rh negative (Rh-). About 85% of Americans have Rh+ blood. Rhesus refers to another type of antigen, or protein, on the surface of red blood cells. The name Rhesus comes from Rhesus monkeys, in which the protein was first discovered.
Facts about Blood Types
- Blood type is inherited, just like hair color.
- Certain blood types are more common in certain countries. In China, over 99 percent of the population has Rh+ blood.
- Different kinds of animals have different kinds of blood. Dogs have 4 blood types; cats have 11; cows have about 800.
- Some people think blood type tells about personality. Legend has it that Type A is calm and trustworthy; Type B is creative and excitable; Type AB is thoughtful and emotional; and Type O is a confident leader.
Blood transfusions are one of the most frequent lifesaving procedures hospitals do. Every 2 seconds someone needs a blood transfusion. So there's always a need for blood donors. One blood donation can save up to three lives. If you'd like to help, contact your community blood center. It's one way to be an everyday superhero and save lives!