Donor Type: O− O+ A− A+ B− B+ AB− AB+ Recipient Type: O− O+ A− A+ B− B+ AB− AB+

Check Compatibility

ABO and Rh Compatibility Matrix

Donor \ Recipient	O−	O+	A−	A+	B−	B+	AB−	AB+

Understanding Blood Type Compatibility

Safe blood transfusion depends on matching certain molecules on the surface of red blood cells with antibodies circulating in the recipient's plasma. The most significant of these molecules belong to the ABO system, which categorizes blood as type A, B, AB, or O based on which antigens appear on cell membranes. A second classification, the Rh factor, indicates the presence (+) or absence (−) of the D antigen. Combining these systems yields eight common blood types. The calculator below applies the standard rules to quickly determine whether one person's blood can be safely given to another.

The immune system is wired to recognize and attack foreign antigens. People with type A blood naturally produce anti‑B antibodies; type B individuals produce anti‑A antibodies. Type O blood lacks both A and B antigens but carries both antibodies. Type AB cells display both antigens yet normally produce neither antibody, making AB individuals universal recipients. When incompatible blood is transfused, the recipient's antibodies bind to the donor's red cells, causing them to clump and rupture, a dangerous reaction called hemolysis. Avoiding this scenario is the primary goal of compatibility testing.

Mathematically, compatibility can be expressed as the set relationship $A\cap B=\varnothing$, where $A$ represents the donor's surface antigens and $B$ represents antibodies present in the recipient's plasma. If the intersection is empty, no antibodies react with donor antigens and the transfusion proceeds safely. When the intersection is not empty, agglutination occurs. This conceptual model highlights why type O negative is considered the universal donor: its set of antigens is empty, so the intersection with any recipient's antibodies also remains empty.

The Rh factor follows similar logic but concerns only the D antigen. Individuals with Rh positive blood express the D antigen and therefore cannot donate to someone with Rh negative blood who may have anti‑D antibodies from previous exposure. However, Rh negative donors can usually give to Rh positive recipients because the absence of the D antigen means there is nothing for anti‑D antibodies to attack. Combining ABO and Rh rules yields a straightforward algorithm that our script implements entirely within your browser.

The calculator also generates a compatibility matrix for reference. Each cell of the table displays "Yes" if the donor type listed in the row can safely provide blood to the recipient type listed in the column, or "No" if it would cause a reaction. Hovering over the matrix after calculation can reinforce your understanding of the underlying rules. Because the data is encoded directly in the page, it runs offline, making it a handy tool for education and quick practice questions even without an internet connection.

To use the tool, pick a donor blood type and a recipient blood type from the drop‑down menus and click the Check Compatibility button. The script parses the ABO and Rh components of each selection, compares them using a series of logical tests, and prints a sentence explaining whether the transfusion is considered safe. If compatible, it confirms the match; if not, it warns that the recipient would likely mount an immune response. You can experiment with all combinations to see how universal donor and universal recipient scenarios emerge from the basic antigen-antibody interactions.

The table below the result area follows standardized guidelines. In practice, transfusion services perform additional testing, including crossmatching specific donor and recipient samples to identify rare antibodies not captured by ABO and Rh typing. They also consider other antigen systems such as Kell, Duffy, and Kidd when necessary. Nevertheless, understanding the core ABO/Rh framework provides a solid foundation for appreciating more nuanced compatibility assessments.

Historically, the development of blood typing revolutionized medicine. Before Karl Landsteiner identified the ABO groups in 1901, transfusions were perilous and often fatal. Once scientists recognized that reactions occurred when unmatched blood was used, they devised simple laboratory tests to determine a person's type. The later discovery of the Rh factor in 1940 further reduced transfusion complications, particularly for pregnant women at risk of hemolytic disease of the newborn. Modern calculators like this one build on that century of research, translating complex immunology into quick answers.

Knowing your blood type also has implications beyond emergency transfusions. It can guide safe organ donations, inform mothers about Rh incompatibility risks during pregnancy, and even influence disease susceptibility research. Some studies explore correlations between ABO type and certain infections or cardiovascular conditions. While the significance of these associations remains under investigation, they illustrate how deeply intertwined blood groups are with human biology. The calculator's explanations aim to demystify the science so you can engage in informed conversations with healthcare professionals.

Always remember that this tool provides educational guidance rather than a medical guarantee. Hospitals rely on laboratory crossmatching and patient history to ensure absolute safety. Variations such as weak D expression, rare antigens, or prior sensitization can alter compatibility in ways a basic algorithm cannot predict. Use the calculator as a learning aid, and defer to medical experts for actual transfusion decisions. With that context in mind, practicing with the calculator can reinforce how antigen patterns and antibodies interact, deepening your appreciation for the lifesaving science of blood typing.