Blood Type Compatibility Chart

How to Use the Blood Type Compatibility Chart

1. 1Select a blood type from the eight ABO + Rh combinations.
2. 2See the list of types that person can safely receive from (as a recipient).
3. 3See the list of types that person can donate to, plus each type's population frequency.
4. 4Cross-reference the full 8×8 matrix to trace any donor-recipient pairing at a glance.

Worked Example: Why O− Is the Emergency Blood

Picture an unconscious trauma patient whose blood type is unknown. There is no time to type and crossmatch, so the transfusion team reaches for O−. Trace it in the chart: O− red cells carry no A antigen, no B antigen, and no Rh antigen, so no recipient's antibodies have anything to attack — O− can donate to all eight types. That universal reach is why it is stocked for emergencies, and why O− donors are always in demand despite being only about 7% of the population.

Now flip the logic to AB+, the universal recipient. An AB+ person makes no anti-A, anti-B, or anti-Rh antibodies, so the chart shows they can receive from every type — but they can donate red cells only to other AB+ people. Notice the pattern the matrix makes visible: the ability to give broadly and the ability to receive broadly are opposite ends of the same antigen logic. O− gives to all but receives only O−; AB+ receives from all but gives only to AB+. (Plasma compatibility runs the reverse direction — AB is the universal plasma donor.)

How Blood Types Are Determined

Your blood type comes from two independent antigen systems on the surface of your red blood cells. The ABO system is defined by whether you carry the A antigen, the B antigen, both (type AB), or neither (type O). The Rh system adds a separate antigen, the Rh (or D) factor: having it makes you positive, lacking it makes you negative. Combining the four ABO groups with Rh-positive or Rh-negative gives the eight blood types — A+, A−, B+, B−, AB+, AB−, O+, and O−. The key to compatibility is that your plasma naturally contains antibodies against any A or B antigen you do not have, ready to attack foreign red cells that carry it. This is the entire basis of transfusion matching, and it is why the chart's donor and recipient lists follow such a clear pattern.

Why Compatibility Is Life-or-Death

Blood-type matching is not a formality — a mismatch can be fatal. If a patient receives red cells carrying an antigen their plasma has antibodies against, those antibodies bind the donor cells and cause agglutination (clumping) and haemolysis (the cells rupturing). The result can be an acute haemolytic reaction leading to shock, kidney failure, and death. This is why O− is the universal red-cell donor: carrying no A, B, or Rh antigen, its cells present nothing for any recipient's antibodies to attack, making it the blood of choice in emergencies where there is no time to type the patient. At the opposite pole, AB+ is the universal recipient, producing no anti-A, anti-B, or anti-Rh antibodies and so able to receive from anyone. Notice the mirror-image logic the matrix reveals: the power to give broadly and to receive broadly sit at opposite ends of the same antigen rules.

Plasma, Pregnancy, and Real-World Testing

Two important nuances go beyond the basic red-cell chart. First, plasma compatibility runs in reverse: because plasma carries the antibodies rather than the antigens, AB is the universal plasma donor while O is the universal plasma recipient — the opposite of the red-cell rules. Second, the Rh factor matters greatly in pregnancy: if an Rh-negative mother carries an Rh-positive baby, she can develop antibodies that threaten a future Rh-positive pregnancy, a risk managed with a preventive injection. Finally, remember that this chart is an educational reference to the general ABO and Rh rules. Real transfusions require laboratory crossmatching, which tests a specific donor unit against a specific patient's blood to catch rarer antibodies the ABO and Rh systems do not cover. Compatibility decisions in medicine are always made by trained professionals with that testing, never from a chart alone.

The Discovery That Made Transfusions Safe

For most of history, blood transfusions were a deadly gamble. Attempts to transfuse blood between people — and even from animals to humans — often ended in catastrophe, with patients suffering violent reactions no one understood. The mystery was solved at the turn of the 20th century by the Austrian physician Karl Landsteiner, who discovered that human blood comes in distinct types and that mixing incompatible types causes the red cells to clump together. He identified the ABO groups, explaining why some transfusions worked and others killed.

Landsteiner's discovery, which earned him a Nobel Prize, transformed medicine: for the first time, transfusions could be made safe by matching donor and recipient. The Rh factor was identified decades later, completing the picture that underlies the compatibility chart on this page. Every safe transfusion performed today rests on that foundational insight — that the antigens on red blood cells, and the antibodies in plasma, determine who can safely give blood to whom.

How Blood Type Is Inherited

Your blood type is inherited from your parents through genes, and the ABO system is a classic example of how genetics works. You carry two copies of the ABO gene, one from each parent, and each copy can be A, B, or O. A and B are codominant — if you inherit one of each, you are type AB and express both antigens. O is recessive, so you are type O only if you inherit an O from both parents. This means an A parent and a B parent can have a child of any type at all — A, B, AB, or O — depending on the hidden copies each carries.

This inheritance pattern has real-world consequences and dispels a common myth. Two type-O parents can only have type-O children, but two type-A parents can have a type-O child if both secretly carry an O copy. Because of these hidden recessive genes, blood type alone can occasionally rule out a biological parent but can rarely prove parentage — which is why blood typing was historically used in paternity questions but has been entirely superseded by DNA testing. The Rh factor is inherited separately, with Rh-positive being dominant over Rh-negative.

Blood Types Around the World

Blood types are not evenly distributed across the human population, and the pattern varies strikingly by region. Globally, type O is the most common, followed by type A, with B less common and AB the rarest. But the proportions shift dramatically depending on where you look: type B is far more common in parts of Asia than in Europe, some Indigenous populations of the Americas are almost entirely type O, and Rh-negative blood is much rarer in Asian and African populations than in European ones.

These differences are thought to reflect thousands of years of evolution, migration, and the influence of diseases that interacted with particular blood-group antigens. For medicine, the practical upshot is that the demand for specific blood types varies by region, and that patients from certain backgrounds — especially those needing rare types — are best served by donors from similar populations. It is one reason blood services actively encourage donation across all communities.

Why Every Blood Type Is Needed for Donation

It is easy to assume that only O-negative — the universal red-cell donor — really matters, but a functioning blood supply needs every type. While O-negative is precious for emergencies, it is a small fraction of the population and cannot meet all demand on its own. Most transfusions use type-matched blood, so a hospital needs a steady supply of every group to serve the patients who have them. Type-O donors are always in high demand simply because O is common and O-negative is universally usable, but A, B, and AB donors are equally essential for the many recipients who share their type.

There is also more to donation than whole red cells. Plasma and plateletsare donated separately and follow their own compatibility rules — recall that for plasma the logic reverses, making AB the universal plasma donor. Because blood components have short shelf lives and cannot be manufactured, supplies depend entirely on regular voluntary donors. Knowing your own type, and understanding the chart above, is a small step toward appreciating why blood donation of every type saves lives — and why services never have enough. As always, this page is an educational reference; real transfusion decisions rest on laboratory crossmatching performed by medical professionals.