ABO and RhD Compatibility Checker
ABO and RhD Compatibility Checker
Check a donor unit against a recipient for ABO and RhD with the component type as an input — because red cells and plasma have opposite rules and platelets have a third set. Group O red cells are the universal donor; group AB plasma is. This is not a crossmatch and not the bedside check.
ABO / RhD compatibility
Component + both groupsComponent: plasma (FFP). Recipient: group A, D negative, a woman of childbearing potential. Unit: group O, D positive
Why the component changes the answer
Plasma — the unit must carry no anti-A or anti-B that will meet the recipient’s red cells. That is the same requirement pointing the other way, which is why group O is universal for one and group AB for the other.
Platelets — both apply at once: the platelets carry antigens, and the plasma they are suspended in carries antibodies.
- group O red cells
- carry neither A nor B, so nobody’s anti-A or anti-B can find them. Universal donor for red cells. Group O plasma is the opposite: it carries both antibodies and may only be given to a group O recipient
- group AB plasma
- carries neither anti-A nor anti-B, so it is safe against any recipient’s red cells. Universal donor for plasma. Group AB red cells are the opposite: they carry both antigens and may only be given to a group AB recipient
- the RhD antigen
- sits on red cells, so it governs red cell selection absolutely and platelet selection only through the residual red cells in the component. It has no bearing at all on plasma, which is why the D selectors go quiet when the component is plasma
- what this page cannot see
- anti-K, anti-Jka, anti-Fya, anti-c, anti-E and every other alloantibody. ABO and D are two systems out of more than forty; the antibody screen and the crossmatch cover the rest, and nothing here replaces them
Worked example
Component: plasma (FFP). Recipient: group A, D negative, a woman of childbearing potential. Unit: group O, D positive
The recipient is group A, so her red cells carry the A antigen and her own plasma contains anti-B
The unit is group O, so its plasma contains both anti-A and anti-B
The donor's anti-A would meet the recipient's A-positive red cells → incompatible
A group A recipient may receive group A or group AB plasma, and nothing else
Now change one selector. Set the component to red cells and the same two units become ABO-perfect: group O red cells carry neither antigen, and a group A recipient may receive them
That pairing then fails on D instead — a D-positive unit into a D-negative woman of childbearing potential, the one D mismatch that is never acceptable if a D-negative unit can be found
One selector, two opposite answers, both correct. That is why the component type belongs on the page, and why a compatibility grid without it is unsafe
The compatibility grid, cell by cell
| Recipient group | Acceptable red cells | Acceptable plasma | Preferred platelets |
|---|---|---|---|
| O | O only | O, A, B, AB — any group | O; A or B acceptable with titre screening |
| A | A, O | A, AB | A; O or AB acceptable with titre screening |
| B | B, O | B, AB | B; O, A or AB acceptable with titre screening |
| AB | AB, A, B, O — any group | AB only | AB; any group acceptable with titre screening |
RhD, by component
| Component | What RhD does here | A D-positive unit into a D-negative recipient |
|---|---|---|
| Red cells | Governs selection absolutely — the D antigen is on the cells being given | Avoid. Never in a female of childbearing potential if D-negative stock exists, and never in anyone with known anti-D. Accepted in adult males and women past childbearing potential when supply is short or bleeding is life-threatening |
| Plasma | Irrelevant — a plasma component carries no red cells | Not applicable. Plasma of any RhD type may be given regardless of the recipient’s D type, and no anti-D prophylaxis is needed |
| Platelets | Matters only through the residual red cells in the component | Acceptable. Give 250 IU anti-D immunoglobulin to a D-negative girl or woman of childbearing potential — enough to cover up to five adult doses within six weeks. Not required for D-negative boys under 18, patients who already have anti-D, or transfusion-dependent adults, for whom D-negative platelets are simply preferred |
Two grids that are mirror images, and a third case that is neither
Almost every ABO chart a clinician meets is a red cell chart. It says group O is the universal donor and group AB the universal recipient, and for red cells that is exactly right: group O cells carry neither the A nor the B antigen, so no recipient’s naturally occurring anti-A or anti-B can find them. The trouble starts when the same sentence is carried across to plasma, where it is precisely inverted. A plasma component’s danger is not its antigens but its antibodies. Group O plasma contains both anti-A and anti-B, so it can be given only to a group O recipient, and the universal plasma donor is group AB, whose plasma contains neither. Set the two grids side by side and they are mirror images of each other. That is why this page asks for the component before it asks for anything else, and why a compatibility table published without a component column is not a shortcut but a hazard.
Platelets are a third case again, and they are the case people find hardest, because both mechanisms apply at once. The platelets themselves carry A and B antigens, so a group A platelet given to a group O recipient meets that recipient’s anti-A and is cleared — a major mismatch, which costs you the increment. And the platelets arrive suspended in donor plasma, so a group O platelet given to a group A recipient delivers passive anti-A straight into the circulation — a minor mismatch, which risks haemolysis of the recipient’s own red cells. Neither is an absolute bar. The British Society for Haematology accepts ABO-incompatible platelets to reduce wastage, and mitigates the haemolysis risk by screening components for high-titre haemagglutinins and by suspending platelets in additive solution rather than plasma. What the guideline does ask is that hospitals build a strategy to give ABO-compatible platelets to the patients who come back for them repeatedly, because it is in those patients that mismatched increments accumulate into a diagnostic problem that looks like refractoriness and is not.
RhD is a separate axis and it behaves differently again in each component. For red cells it is decisive, because the D antigen is on the cells being transfused: a D-negative person exposed to D-positive red cells may form anti-D, permanently, and in a girl or woman of childbearing potential that antibody causes haemolytic disease of the fetus and newborn in a later pregnancy. That single consideration is why national blood services reserve O D negative red cells for children and for females under 51 and push adult men towards O D positive in an emergency — NHS Blood and Transplant has called amber alerts on O D negative supply twice in recent years, and the reservation is what keeps the stock where it is irreplaceable. For platelets, D matters only through the handful of residual red cells in the component, so D-positive platelets may be given to a D-negative recipient, with 250 IU of anti-D immunoglobulin covering up to five adult doses over six weeks in a girl or woman of childbearing potential, and no prophylaxis needed at all in the other D-negative groups. For plasma, D does not matter: there are no red cells in the bag, so plasma of any RhD type may be given to any recipient and no prophylaxis follows.
Finally, the limit of this page. It knows two blood group systems out of more than forty. It cannot see anti-K, anti-Jka, anti-Fya, anti-c or anti-E, and those are the antibodies behind most delayed haemolytic transfusion reactions; they are detected by the antibody screen and honoured by the crossmatch, and a patient who has one needs antigen-negative units that no ABO grid can identify. It also cannot tell you whether the unit in your hand is the unit issued for this patient. That is the job of the final identity check, performed by the person administering the component, at the patient’s side, immediately before it is given, matching the details on the component against the patient’s identification band — last name, first name, date of birth and unique patient identification number. Wrong-blood-into-patient incidents are overwhelmingly identification failures rather than laboratory failures, which means the bedside check is where an ABO-incompatible transfusion is actually prevented. Use this page to understand the rules; use the laboratory and the bedside check to apply them.
Frequently asked questions
Why is group O the universal donor for red cells but not for plasma?
Because the two components are dangerous for opposite reasons. A red cell unit is dangerous if it carries an antigen the recipient has an antibody to, and group O red cells carry neither A nor B, so nobody’s anti-A or anti-B can find them — universal donor. A plasma unit is dangerous if it carries an antibody that will meet the recipient’s red cells, and group O plasma carries both anti-A and anti-B, so it can only be given to a group O recipient. The universal plasma donor is group AB, whose plasma has neither antibody. The two grids are exact mirror images: group O is at one extreme for red cells and the other extreme for plasma, and group AB the reverse.
Which blood groups can a group A patient receive?
Red cells: group A or group O, because a group A patient has anti-B and neither A nor O cells carry the B antigen. Plasma: group A or group AB, because a group A patient’s red cells carry the A antigen and only A and AB plasma are free of anti-A. Platelets: group A is ideal; group O or AB platelets are acceptable in practice but each is imperfect in a different way — group O platelets carry passive anti-A, so they should be screened for high-titre haemagglutinins, and group AB platelets carry the B antigen, so the increment will be lower. Notice that the answer for red cells and the answer for plasma have only group A in common, which is why the component must be stated.
Do platelets have to be RhD matched?
Not in the way red cells do. Platelets carry no D antigen; the risk comes from the few residual red cells in the component. The British Society for Haematology asks that RhD negative girls and women of childbearing potential receive RhD negative platelets, and that if none are available RhD positive platelets may be given with anti-D prophylaxis — the BCSH dose is 250 IU, enough to cover up to five adult therapeutic doses within six weeks, given subcutaneously or intravenously if the platelet count is 30 × 10⁹/L or below. For RhD negative boys under 18, patients who already have anti-D and transfusion-dependent adults, RhD negative platelets are preferred but RhD positive platelets should be given if negative ones are unavailable, and anti-D prophylaxis is not required.
Does fresh frozen plasma need to be RhD matched?
No. Plasma of any RhD type may be transfused regardless of the recipient’s RhD type, and anti-D prophylaxis is not needed afterwards, because a plasma component contains no red cells and therefore no D antigen. The same applies to cryoprecipitate. Plasma is still matched for ABO, and that part matters very much: group O plasma into a group A, B or AB recipient is an ABO-incompatible transfusion.
Does this page replace the crossmatch?
No, and it cannot. It knows the ABO and RhD systems only — two out of more than forty blood group systems — so it is blind to anti-K, anti-Jka, anti-Fya, anti-c, anti-E and the other clinically significant alloantibodies that cause delayed haemolytic transfusion reactions and that require antigen-negative units. Those are found by the antibody screen and honoured by the crossmatch or by an electronic issue algorithm that has already checked them. Nor can this page tell you that the unit in front of you is the unit issued for this patient: that is the final identity check, done at the patient’s side immediately before administration, and it is where wrong-blood-into-patient incidents are actually caught.
What happens if ABO-incompatible red cells are transfused?
The recipient’s naturally occurring anti-A or anti-B binds the transfused cells and activates complement, producing acute intravascular haemolysis. It can begin after only a few millilitres. The features are fever, rigors, pain in the loin, back, chest or abdomen, hypotension, haemoglobinuria, and oozing from venepuncture sites as disseminated intravascular coagulation develops; acute kidney injury and death follow in severe cases. The immediate response is to stop the transfusion, keep venous access open with saline, and check the identity of the patient against the component — and then to treat and investigate. The transfusion reaction interpreter covers the rest of the acute differential.
Related calculators
References
- Kahwaji J, Vo AA, et al. Pretransfusion Testing. In: StatPearls. NCBI Bookshelf NBK585033. Table 2, blood product selection compatibility chart: group O patients — compatible RBC O, compatible plasma O, A, B, AB; group A — RBC A, O, plasma A, AB; group B — RBC B, O, plasma B, AB; group AB — RBC AB, A, B, O, plasma AB. “All plasma-containing components should be compatible with the recipient’s red cells. All products containing more than 2 ml of red cells must be ABO compatible with the recipient’s plasma.”
- Estcourt LJ, Birchall J, Allard S, et al. Guidelines for the use of platelet transfusions. British Society for Haematology; Br J Haematol. 2017;176(3):365–394. ABO-compatible platelets should be maximised for patients needing regular support (2B); ABO-incompatible platelets acceptable to reduce wastage, with high-titre-negative and non-group-O components carrying a lower risk of haemolysis; RhD negative girls and women of childbearing potential should receive RhD negative platelets, or RhD positive with anti-D prophylaxis; for RhD negative boys under 18, patients with existing anti-D and transfusion-dependent adults, anti-D prophylaxis is not required.
- Qureshi H, Massey E, Kirwan D, et al. BCSH guideline for the use of anti-D immunoglobulin for the prevention of haemolytic disease of the fetus and newborn. Transfus Med. 2014;24(1):8–20. “A dose of 250 IU anti-D immunoglobulin should be sufficient to cover up to five adult therapeutic doses of D positive platelets given within a 6-week period”; subcutaneous or intravenous administration when the platelet count is 30 × 10⁹/L or below; intravenous anti-D preferred after more than 15 mL of D-positive red cells; residual D-positive cells quantitated by flow cytometry at 48 h after an intravenous dose or 72 h after intramuscular.
- Harris AM, Atterbury CLJ, Chaffe B, et al. Guideline on the Administration of Blood Components. British Committee for Standards in Haematology. “The healthcare professional who administers the blood component must perform the final administration check. This check must be performed at the patient’s side immediately before administering the blood component by matching the patient details attached to the blood component with the details on the patient’s identification band.” Minimum identifiers: last name, first name, date of birth and unique patient identification number.
- Australian Red Cross Lifeblood. Component compatibility. Red cells — O to O; A to A, O; B to B, O; AB to AB, A, B, O. Plasma — O to any group; A to A, AB; B to B, AB or low-titre A; AB to AB or low-titre A. “Plasma of any RhD type may be transfused regardless of recipient RhD type.”
- National Advisory Committee on Blood and Blood Products (Canada). Utilization and Inventory Management of Group O RhD Negative Red Blood Cells. “Group O RhD negative individuals of child-bearing potential should receive only RhD negative components”; “Individuals alloimmunized against RhD antigen must receive RhD negative RBCs, unless extenuating circumstances exist.”
- NHS Blood and Transplant. Group O red cells — appropriate use of blood components. O D negative red cells are reserved for children and females under 51 in the emergency red cell specification, with O D positive directed to males over 18; amber alerts were called on O D negative supply in 2022 and 2024.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.