Every person has a unique blood type because the immune cells (antigens) on their red blood cells differ. The discovery of blood types in 1901 saved many lives and permanently changed medicine. Four main blood types exist: A, B, AB, or O, and everyone has a positive or negative Rh factor.
Blood types are important because they affect blood transfusions, pregnancy outcomes, and blood donation. This article outlines the different blood types and their practical application in blood donation and medical care.
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How Blood Types Are Determined
Blood is made up of erythrocytes (red blood cells) that bind to oxygen and carry it throughout the body. Each red blood cell (RBC) has a specific compound that can trigger an immune response; these are called antigens and can be further classified as A, B, AB, or O.
The immune system produces antibodies, identifying and attacking antigens (foreign molecules). If the wrong blood type is infused, the body can attack the foreign antigen and cause an immune response (transfusion reaction).
There are eight main blood types:
- A positive (A+)
- A negative (A-)
- B positive (B+)
- B negative (B-)
- AB positive (AB+)
- AB negative (AB-)
- O positive (O+)
- O negative (O-)
In addition to the antigen blood typing system, there are proteins on the surface of RBCs called Rh factor. If a person has Rh factor, they have a positive blood type; if they do not have Rh factor, they have a negative blood type.
This is combined with the A, B, and O typing systems to create a unique blood type (e.g., O+). Rh factor is especially important to identify in pregnancy because the immune cells of the mother may attack the baby and potentially cause hemolytic disease in the newborn. If you are pregnant, talk to your medical provider about Rh factor compatibility and fetal safety.
The most common blood type is O+, 38% of the population has this antigen/rH factor combination. Types A and B are the next most common types. Type AB is the least common worldwide.
Type O is given during an emergency when the patient's blood type is unknown. It can be given to anyone and is called the “universal donor” blood type. Interactive tools are available to learn the prevalence of a certain blood type.
Rare Blood Types and Their Significance
A unique combination of antigens makes a blood type rare. A rare blood type lacks the antigens most others (99%) are positive for. The rarest blood type, AB-, is present in 1% of Caucasians, 0.3% of African Americans, 0.1% of Asians, and 0.2% of Latino Americans.
One of the rarest blood types is Bombay, first discovered in India. The Bombay blood group is unique because people with it have certain antibodies (anti-A, anti-B, and anti-H) in their blood. These antibodies cause their blood to react with all other blood types, which means their blood cannot mix safely with any other group. This makes it very hard for them to get blood transfusions unless the donor also has the rare Bombay blood type.
Several factors, including genetics and geography determine blood type. Your parents also determine it and is typically affected by ethnic heritage.
The Golden Blood Type (Rh Null)
There is an extremely rare blood type called Rh Null, meaning there are no Rh antigens on the blood cell surface. This is called the “golden blood type,” and fewer than 50 people have been identified with it.
Blood Types and Donation
The blood supply is a vital aspect of the healthcare system; roughly 29,000 units of RBCs are needed daily in America. Blood can only come from donors; it cannot be manufactured. A person injured in a motor vehicle crash may need as many as 100 units of red blood cells.
Blood type compatibility in donations is critical to ensure safety and prevent adverse reactions. Blood transfusions work like a matching system. Your blood type—A, B, AB, or O—depends on proteins (antigens) in your red blood cells. If you receive the wrong blood type, your immune system attacks it, causing dangerous reactions.
People with O-negative blood are “universal donors” because their blood has no antigens, so it’s safe for anyone. People with AB-positive blood are “universal recipients” because they can safely receive any type of blood.
Which Blood Types Are in Demand?
Type O blood is always in high demand because it is the universal donor and most widely used by hospitals. However, because only 7% of people have this blood type, it is always in demand. Similarly, only 4% of people have AB (universal recipient) blood, which is also in demand.
If you want to donate blood, visit the Red Cross website to find a drive near you and review the eligibility requirements.
How to Determine Your Blood Type
Knowing your blood type is useful information for patient self-advocacy and in case of an emergency. There are several ways to determine your blood type, the most common being lab testing ordered by a medical provider. Point-of-care (quick result) blood type testing kits can be used at home, but caution should be used because the accuracy of these tests is still being studied.
Blood Type Charts and Visual References
Because of the immune cells present in red blood cells, only certain blood types are compatible with transfusions.
Compatibility Chart for Blood Transfusions
The chart below outlines the recipient's blood type and what type of donor blood is safe for transfusion.
Blood transfusion in the clinical setting involves strict protocols to ensure patient safety.
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Key Takeaways
- Understanding your blood type is crucial for safe medical care and emergencies.
- Blood type is determined by red blood cell antigens and Rh factor; this makes the ABO and Rh positive or negative blood type system.
- There are eight main blood types, some of which are rarer than others.
- Rh factor compatibility is especially important in pregnancy and delivery of the baby.
- Not all blood types are compatible, so matching the right type saves lives.
- O- blood can be given to anyone, making it vital in emergencies.
- AB+ blood type individuals are universal recipients, meaning they can receive any type of blood in a transfusion.
- A single donation can help save multiple lives.
- Blood donations are constantly needed for accidents and surgeries.
- Find a donation center near you and consider donating blood to help those in need.
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