Blood Type Guide: Compatibility, Genetics, Transfusion

Author: Ian C. Langtree - Writer/Editor for Disabled World (DW)
Published: 28 Sep 2012 - Updated: 30 Aug 2026
Publication Type: Charts, Graphs, Tables

Table of Contents:
Synopsis - Definition - Overview - FAQs - Insights, Updates - Related Content

Synopsis

This information presents essential facts and charts about human blood types, including the ABO and Rh systems, and explains how the presence or absence of specific antigens on red blood cells determines compatibility for blood transfusions. It details which blood types can safely donate to or receive from others, emphasizing the importance of matching blood types to prevent dangerous reactions. The information is authoritative due to its clear presentation of widely accepted medical facts and practical charts, making it useful for anyone needing to understand blood type basics - including individuals with disabilities or seniors who may require transfusions or wish to know more about their own health.

At a Glance

• 1 - Around 5 million Americans need blood transfusions every year. The average adult body holds about four to six liters, or 7 to 10.5 pints, of blood.
• 2 - The International Society of Blood Transfusion now recognizes 48 separate blood group systems. The ABO and Rh systems are only two of the most familiar among them.
• 3 - Austrian scientist Karl Landsteiner first classified blood in the early 20th century by spotting two molecules he labeled A and B. His discovery of these antigens made safe transfusions possible.
• 4 - Before DNA analysis existed, blood typing was the main tool used in paternity testing to rule a man out as a possible father. For example, a man with type AB blood cannot father a child with type O blood.

Topic Definition

Blood Type

A blood type, also called a blood group, is the classification of a person's blood based on the presence or absence of inherited antigens on the surface of their red blood cells. The two systems most people know are ABO, which sorts blood into A, B, AB, and O based on the A and B antigens, and Rh, which adds a positive or negative label depending on whether the Rh factor is present. These antigens matter because the body will attack red cells it does not recognize, so a mismatched transfusion can cause cells to clump and block blood vessels. That is why donors and recipients are carefully matched, with type O negative often described as the universal red cell donor and type AB positive as the universal plasma donor. Because these traits are passed from parents to children, blood types also carry genetic information that has long been used in studies of inheritance and, historically, in paternity testing.

Overview

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".

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".

Frequently Asked Questions

What is the rarest blood type in the world?

AB negative is generally considered the rarest of the eight common blood types, found in a very small share of the population. Rarity varies by region and ethnic background, so the least common type is not the same everywhere.

Can my blood type change during my lifetime?

Your inherited blood type stays the same throughout life under normal circumstances. Rare exceptions can occur after a bone marrow transplant or certain illnesses that affect blood cell production.

How do I find out my blood type?

A simple blood test ordered by a doctor or offered at many blood donation centers will identify your ABO and Rh type. Donating blood is one of the most common ways people learn their type for free.

Why is Rh factor important during pregnancy?

If an Rh negative mother carries an Rh positive baby, her immune system may react to the baby's blood in some cases. A preventive injection can stop this reaction and protect future pregnancies.

Does blood type affect diet or nutrition needs?

Popular blood type diet theories claim certain foods suit specific types, but mainstream research has not supported these claims. Nutrition advice is generally based on overall health rather than blood group.

Which blood types are most compatible for pregnancy between partners?

Most blood type combinations between partners are perfectly safe for pregnancy. The main consideration is Rh compatibility, which doctors monitor and manage with routine care.

Can two parents with type O blood have a child with a different type?

Two type O parents will have type O children, since neither can pass on an A or B antigen. Other combinations of parent types can produce a wider range of outcomes in their children.

How long can donated blood be stored before use?

Red blood cells can typically be stored refrigerated for up to about 42 days, while platelets last only a few days. Plasma can be frozen and kept for around a year, depending on local standards.

Insights, Analysis, and Developments

Editorial Note: The exploration of blood types in this article underscores the critical role of medical science in everyday life, from ensuring safe transfusions to unraveling genetic connections between generations. Its clear, concise presentation demystifies a complex topic, making it accessible to all, including those managing chronic conditions or disabilities who may face frequent medical interventions. By bridging scientific rigor with practical application, the article serves as a reminder of how foundational knowledge can directly impact personal health decisions, fostering informed choices in an increasingly complex healthcare landscape.

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.