Blood Type Compatibility Chart

Why blood types have to match at all

Red blood cells carry markers on their surface called antigens. The two that matter most are A and B, and the third is the Rh factor, usually written as plus or minus. Your immune system makes antibodies against whichever of those antigens you do not have.

• Type A blood has the A antigen and makes anti-B antibodies.
• Type B blood has the B antigen and makes anti-A antibodies.
• Type AB has both antigens and makes neither antibody.
• Type O has neither antigen and makes both antibodies.

The Rh factor sits on top of that: Rh-positive blood carries the D antigen, Rh-negative blood does not and can make anti-D. Give someone a blood type whose antigens their antibodies recognize, and the red cells are destroyed, which is why compatibility matters and why the American Red Cross blood types reference is written the way it is.

The table below is the standard ABO and Rh reference. It is a chart, not a diagnosis: real transfusions also depend on more than 600 other red cell antigens, and hospitals confirm every unit with their own typing and crossmatch.

Red cell compatibility: who can receive what

Read this table as a recipient. Find your blood type on the left and the safe red cell donors are listed on the right.

Two patterns make the table easy to remember. Negative recipients can only take negative blood, because an Rh-negative person can make anti-D antibodies. And O recipients can only take O blood, because O blood makes both anti-A and anti-B. Everything else follows from those two rules. AB positive, sitting at the bottom with no antibodies at all, can take anything.

From the donor's side: who you can help

Flip the table around and the same rules describe who your donation can be given to.

• O negative, red cells can go to all eight types. The universal red cell donor, and the type emergency rooms keep stocked.
• O positive, red cells go to any positive recipient (O+, A+, B+, AB+), which is about 85% of people.
• A negative, A−, A+, AB−, AB+.
• A positive, A+ and AB+.
• B negative, B−, B+, AB−, AB+.
• B positive, B+ and AB+.
• AB negative, AB− and AB+ only, but AB plasma makes them valuable in a different way.
• AB positive, AB+ only. The rarest type to need, and the most useful as a plasma donor.

In practice, blood centers care about more than rarity. O− is the type most often in short supply because it is used in emergencies before a patient is typed, and O+ is the most useful overall because it is the most common. The World Health Organization's blood safety fact sheet notes that most countries still struggle to collect enough blood to meet demand, which is why regular donors matter more than rare ones.

Plasma and platelets run the other way

Plasma is the liquid part of blood and it carries antibodies, not antigens, so the compatibility rules are the mirror image of the red cell rules. Getting this backwards is the single most common mistake people make with blood type charts.

So AB is the universal plasma donor even though it is the universal recipient for red cells, and O is the universal red cell donor even though O plasma can only go to O recipients. If you are AB positive, you are a rare red cell recipient but a valuable plasma donor; if you are O negative, you are the most needed red cell donor but can only receive O− plasma. Rh status matters much less for plasma than it does for red cells.

Rh and pregnancy: the one case where a mismatch is common

The Rh factor becomes important outside transfusions when an Rh-negative mother carries an Rh-positive baby. During pregnancy or delivery, some of the baby's Rh-positive red cells can enter the mother's circulation, and her immune system may start making anti-D antibodies. The first pregnancy is usually unaffected because the antibodies take time to develop, the risk is mainly to later Rh-positive pregnancies, where those antibodies can attack the baby's red cells and cause anemia.

The standard prevention is anti-D immune globulin, often called RhoGAM. It is typically given around 28 weeks of pregnancy and again within 72 hours of giving birth if the baby is Rh positive, and also after events such as miscarriage, amniocentesis or bleeding. About 15% of Americans are Rh negative, so this is not a rare scenario.

None of this is something to manage from a web page. Rh status in pregnancy is checked by blood tests, and the treatment decisions are your obstetrician's. If you are Rh negative and pregnant, or think you might be, say so at your first appointment.

What this chart cannot tell you

Everything above describes the ABO and Rh systems, which are the two that matter most in practice. They are not the whole story:

• More than 600 antigens exist. Kell, Duffy, Kidd, MNS and others can cause reactions even when ABO and Rh look compatible.
• Your antibodies are individual. People who have had previous transfusions or pregnancies may carry antibodies that a chart cannot predict.
• Hospitals crossmatch. Before a unit is given, the blood bank mixes a sample of the patient's serum with donor red cells to confirm they get along. That test, not this table, is what makes a transfusion safe.
• Emergencies are different. In a crisis, O negative red cells may be given before the patient's type is known, precisely because they work for everyone.

So use this page the way it is meant to be used: to understand why AB+ can take anything, why O− can take only O−, and why plasma runs backwards. For anything that affects you personally, a transfusion, surgery, a pregnancy, a donation, the hospital blood bank's own typing and crossmatch is the only answer that counts. This is a reference estimate of the standard rules, not medical advice, and it cannot replace testing done on your own blood.