Blood Type Guide: Compatibility, Genetics & Transfusion

When a person's blood is analyzed under a microscope distinct blood differences are visible. In the early 20th century, an Austrian scientist named Karl Landsteiner classified blood according to those differences. Landsteiner observed two distinct chemical molecules present on the surface of the red blood cells. He labeled one molecule "A" and the other molecule "B".

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Some Quick Facts Regarding Blood Types/Groups

• About 5 million Americans need blood transfusions every year.
• Receiving blood from the wrong ABO group can be life threatening.
• Your body carries around four to six liters (7 to 10.5 pints) of blood.
• Almost half (48%) of the UK population has blood group O, making this the most common blood group.
• Many pregnant women carry a fetus with a blood type which is different from their own, which is not a problem
• A total of 35 human blood group systems are now recognized by the International Society of Blood Transfusion (ISBT).
• A popular belief in Japan is that a person's ABO blood type is predictive of their personality, character, and compatibility with others.
• With regard to transfusions of packed red blood cells, individuals with type O Rh D negative blood are often called universal donors, and those with type AB Rh D positive blood are called universal recipients.

Find out other interesting blood facts in our list of fascinating and amazing human body facts.

Blood Types (Groups)

A blood type (also called a blood group) is defined as the classification of blood based on the presence or absence of inherited antigenic substances on the surface of red blood cells (RBCs). A series of related blood types constitutes a blood group system, such as the Rh or ABO system. The frequencies of the ABO and Rh blood types vary from population to population.

• Blood Type A - If the red blood cell has only "A" molecules on it.
• Blood Type B - If the red blood cell has only "B" molecules on it.
• Blood Type AB - If the red blood cell has a mixture of both "A" and "B" molecules.
• Blood Type O - If the red blood cell has neither "A" or "B" molecule.

There are eight different common blood types, which are determined by the presence or absence of certain antigens, which are substances that can trigger an immune response if they are foreign to the human 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. There are 4 major blood groups determined by the presence or absence of two antigens (A and B) on the surface of red blood cells:

In addition to the A and B antigens, there is a third antigen called the Rh factor, which can be either present (+) or absent ( - ). In general, Rh negative blood is given to Rh-negative patients, and Rh positive blood or Rh negative blood may be given to Rh positive patients.

• The universal red cell donor has Type O negative blood type.
• The universal plasma donor has Type AB positive blood type.

Donating Blood by Compatible Type:

Blood types are very important when a blood transfusion is necessary. In a blood transfusion, a patient must receive a blood type compatible with his or her own blood type. If the blood types are not compatible, red blood cells will clump together, making clots that can block blood vessels and cause death.

If two different blood types are mixed together, the blood cells may begin to clump together in the blood vessels, causing a potentially fatal situation. Therefore, it is important that blood types be matched before blood transfusions take place. In an emergency, type O blood can be given because it is most likely to be accepted by all blood types. However, there is still a risk involved.

Table of the 48 Blood Group Systems

Notes:

* As defined by the HUGO Gene Nomenclature Committee.

† MIC2 product. [] = no gene product on normal RBCs.

Paternity Blood Matches

Paternity can be determined by highly accurate tests conducted on blood or tissue samples of the father - or alleged father, mother and child. Before DNA analysis was available, blood types were the most common factor considered in human paternity testing.

In cases of questioned paternity, ABO blood-typing can be used to exclude a man from being a child's father. An example being, a man who has type AB blood could not father a child with type O blood, because he would pass on either the A or the B allele to all of his offspring. The word "allele", an abbreviated term for "allelomorph" meaning "other form", which was used in the early days of genetics to describe variant forms of a gene detected as different phenotypes.

Paternity testing can be especially important when the rights and duties of the father are in issue and a child's paternity is in doubt. Tests can also determine the likelihood of someone being a biological grandparent.

How accurate are Paternity blood type or DNA tests? According to FindLaw these tests have an accuracy range of between 90 to 99%. Below is a chart showing possible blood type of a child according to their parents blood group(s).

Printable Blood Type Chart

Chart showing compatible blood types for receiving blood transfusions.

To print the charts click "File" and then "Print". Or, use a keyboard shortcut:

Mac: Command-key + p

Windows and Linux: Ctrl + p

In the window that appears, select the destination and change your preferred print settings.

Click "Print".

Insights, Analysis, and Developments

Author Credentials: Ian is the founder and Editor-in-Chief of Disabled World, a leading resource for news and information on disability issues. With a global perspective shaped by years of travel and lived experience, Ian is a committed proponent of the Social Model of Disability-a transformative framework developed by disabled activists in the 1970s that emphasizes dismantling societal barriers rather than focusing solely on individual impairments. His work reflects a deep commitment to disability rights, accessibility, and social inclusion. To learn more about Ian's background, expertise, and accomplishments, visit his full biography.