Why is O negative the universal donor?

O- red blood cells carry no A, B, or RhD antigens. Because there is nothing for a recipient's immune system to attack, O- cells can be transfused into any of the 8 blood groups. This makes O- the universal red-cell donor, critical for emergency transfusions.

Why is AB positive the universal recipient?

AB+ blood carries the A, B, and RhD antigens, so an AB+ person has no antibodies against any of those antigens. They can therefore safely receive red cells from every blood group. AB+ is the universal red-cell recipient.

Does this cover plasma compatibility too?

No. This tool covers red blood cell (RBC) transfusion only. Plasma compatibility runs the opposite direction because plasma carries antibodies rather than antigens, so AB plasma is the universal plasma donor while O is the universal plasma recipient.

How does Rh factor affect compatibility?

Rh positive means the D antigen is present. An Rh-negative recipient must not receive Rh-positive cells because they can form anti-D antibodies, which is especially dangerous in pregnancy. Rh-positive recipients can receive either Rh-positive or Rh-negative cells.

Can I use this for medical decisions?

No. This is an educational reference using the standard ABO/Rh antigen rules. Real transfusions require crossmatching, antibody screening, and other compatibility tests performed by a qualified blood bank. Always defer to clinical professionals.

What is the Blood Type Compatibility Reference?

Look up which blood types can give and receive red blood cells across all 8 ABO/Rh groups. Computed from antigen and antibody logic with a full transfusion matrix and O-/AB+ universal rules. Runs in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Blood Type Compatibility Reference

Name: Blood Type Compatibility Reference
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Blood transfusion safety comes down to a simple antigen rule: a recipient can only receive red blood cells from a donor whose antigens the recipient already carries. This reference computes compatibility for all 8 ABO/Rh blood groups from first principles rather than reciting a fixed chart, and shows the full transfusion matrix at a glance.

How it works

Each red blood cell can carry up to three antigens that matter here: A, B (the ABO system) and RhD (the Rhesus D antigen, which makes a type “positive”). Your immune system makes antibodies against any ABO antigen you do not have, so transfusing cells with a foreign antigen triggers a reaction.

The compatibility rule is therefore: a donor’s red cells are safe for a recipient if every antigen the donor carries is also present on the recipient. The tool derives each type’s antigens (for example AB+ has A, B and RhD; O- has none) and applies this check across all pairs. Because O- carries no antigens it can give to anyone, and because AB+ carries all three it can receive from anyone.

The eight blood groups and their antigens

Blood type	A antigen	B antigen	RhD antigen	Antibodies made
O−	No	No	No	Anti-A, Anti-B
O+	No	No	Yes	Anti-A, Anti-B
A−	Yes	No	No	Anti-B
A+	Yes	No	Yes	Anti-B
B−	No	Yes	No	Anti-A
B+	No	Yes	Yes	Anti-A
AB−	Yes	Yes	No	None
AB+	Yes	Yes	Yes	None

The antibody column explains the mechanism: if you transfuse A antigen into someone who makes Anti-A antibodies, the antibodies attack the donated cells immediately, causing a haemolytic transfusion reaction.

Full red-cell compatibility matrix (who can donate to whom)

Recipient →	O−	O+	A−	A+	B−	B+	AB−	AB+
O−	Yes
O+	Yes	Yes
A−	Yes		Yes
A+	Yes	Yes	Yes	Yes
B−	Yes				Yes
B+	Yes	Yes			Yes	Yes
AB−	Yes		Yes		Yes		Yes
AB+	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes

(Rows = recipient; Columns = donor. “Yes” = the donor’s red cells are safe for that recipient in a standard ABO/Rh-D crossmatch.)

Reading the matrix and notes

Use the direction switch to flip between “I donate” (which recipients can receive your cells) and “I receive” (which donors are compatible with you). Rh-negative recipients are restricted to Rh-negative donors to avoid anti-D sensitisation — particularly critical in females of childbearing age, where anti-D antibodies can cause haemolytic disease of the newborn in a subsequent pregnancy.

A note on plasma: compatibility is reversed for plasma because plasma carries antibodies rather than antigens. AB plasma (no antibodies) is the universal plasma donor, while O plasma requires the most care. This tool models red-cell (RBC) transfusion only.

This is an educational reference. Real transfusions require full crossmatching, extended antigen typing, and antibody screening by a qualified blood bank. Never use this tool to guide clinical decisions.