Hematologist
CION Cancer Clinics
Blood groups and transfusion compatibility, explained | CION Cancer Clinics
For red cells, O negative can usually be given to any group, and AB positive can usually receive from any group. For plasma the rule reverses, and AB plasma suits everyone. Platelets prefer a match but are less strict. The chart shows the usual rules only. Before any transfusion, the blood bank tests the patient's fresh sample against the donor unit, and that test decides. At CION Cancer Clinics, our haematologist cares for anaemia, bleeding, clotting and inherited blood disorders, with ArogyaSri, CGHS and cashless insurance accepted.
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Medically reviewed by Dr. Basudev PokhrelConsultant Haematologist · last reviewed September 2026, next review due September 2027
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On this page
- Which blood groups can safely receive which?
- Which red cells can each group usually receive?
- Why is the rule different for plasma and platelets?
- What checks happen before any blood is given?
- What do the words on the blood bank form mean?
- What do families often believe about blood groups?
- What can a compatibility chart not tell you?
- Common questions about blood group compatibility
The short answer
Which blood groups can safely receive which?
For red cells, O negative can usually be given to anyone, and AB positive can usually receive from anyone. For plasma, the rule runs the other way: AB plasma suits every group. Even with the chart, the blood bank always tests the patient's and the donor's blood against each other before a transfusion.
What a blood group actually is
Your red cells carry markers on their surface, a little like name badges. The ABO system asks whether you carry the A marker, the B marker, both (AB) or neither (O). The RhD system asks whether you carry the D marker. If you do, you are positive. If you do not, you are negative. Put together, that gives the eight common groups written on a report, such as B positive or O negative.
Why a mismatch is dangerous
Your plasma, the liquid part of blood, carries antibodies. These are defence proteins against the markers you do not have. Someone who is group A carries antibodies against B. If B red cells are given to them, those antibodies attack the new cells. That reaction can be serious and fast. The whole purpose of grouping and matching is to stop it happening.
This page explains the general rules. It is not a way to choose blood for a patient. Only the blood bank does that.The chart
Which red cells can each group usually receive?
Read down the left for the patient's group. The right shows the donor groups that are usually suitable for red cells.
Patient's blood group
Red cells usually suitable from
O negative
O negative only
O positive
O positive, O negative
A negative
A negative, O negative
A positive
A positive, A negative, O positive, O negative
B negative
B negative, O negative
B positive
B positive, B negative, O positive, O negative
AB negative
AB negative, A negative, B negative, O negative
AB positive
All eight groups
Not sure whether this applies to you?
Ask an oncologistNot one rule
Why is the rule different for plasma and platelets?
Most transfusions today give one part of the blood, not whole blood. Each part follows its own matching logic.
Red cells
What matters is the markers on the donor's cells. O cells carry no A or B marker, so they rarely trigger the patient's antibodies. That is why O negative red cells are the usual emergency choice.
Often given for
- Severe anaemia, meaning a low haemoglobin
- Heavy bleeding
- Low counts during blood cancer treatment
Plasma
Here the donor's antibodies matter. AB plasma carries no antibodies against A or B, so it suits every patient. O plasma carries both, so it suits only O patients.
Usually suitable
- Group O patient: any plasma group
- Group A patient: A or AB plasma
- Group B patient: B or AB plasma
- Group AB patient: AB plasma only
Platelets
A matching ABO group is preferred, but when stock is short a blood bank may give a different group. RhD type is still watched closely, especially for girls and women who may want children later.
This is why a platelet request may accept more than one group.In the blood bank
What checks happen before any blood is given?
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A fresh sample is taken
Even if you know your group, the hospital takes a new sample and labels it at the bedside. A group on an old card or from memory is never used on its own.
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Grouping
The laboratory confirms the ABO group and RhD type from that sample. Many blood banks check it twice, sometimes on two separate samples.
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Antibody screen
The sample is checked for unusual antibodies. These can develop after earlier transfusions or pregnancies, and the basic chart does not account for them.
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Cross-match
The patient's plasma is tested against the chosen donor unit. If the two react, that unit is not given, whatever the chart says.
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Bedside check
Before the bag is connected, two staff members usually check the patient's name, identity band and the bag label together. Then the patient is watched closely once it starts.
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On the form
What do the words on the blood bank form mean?
- ABO group
- Whether your red cells carry the A marker, the B marker, both or neither.
- Rh or RhD
- Whether your red cells carry the D marker. Written as positive or negative, or +ve and -ve.
- Cross-match or compatibility test
- A laboratory test mixing the patient's sample with a donor unit to confirm they do not react.
- PRBC or packed red cells
- Red cells with most of the plasma removed. The most common transfusion product.
- FFP
- Fresh frozen plasma, the liquid part of blood, frozen to keep its clotting proteins.
- Transfusion reaction
- Any unwanted response during or after a transfusion, from a mild rash to a serious reaction.
Commonly believed
What do families often believe about blood groups?
"Family members always have the same group, so their blood is safest."
Brothers, sisters and children can have a different group from the patient. Blood from close relatives also carries its own rare risks, so blood banks are cautious with it. A matched unit from a screened voluntary donor is just as good.
"O negative is the universal group, so it is always given."
It is used in emergencies when there is no time to test. Otherwise blood banks give the patient's own group. O negative is short in supply and saved for patients who truly need it.
"I know my group from school, so no test is needed."
Groups written on old cards or remembered are sometimes wrong. The hospital tests every patient before every transfusion, and that is a safety step, not a sign of distrust.
"If the group matches, nothing can go wrong."
Matching lowers the risk a great deal. But unusual antibodies, fever reactions and allergic reactions can still happen. That is why the patient is watched during the transfusion, and why you should tell the nurse at once if they feel unwell.
Being straight with you
What can a compatibility chart not tell you?
A chart shows the usual ABO and RhD rules. It cannot tell you whether a particular bag of blood is safe for a particular patient. Only testing in the blood bank can.
Rare groups sit outside the chart
Some people have groups the chart does not show. The Bombay blood group, first described in India, looks like group O on a basic test. These patients can only receive blood from other Bombay group donors. Our page on rare blood groups explains how families find them.
Patients who need blood often
People with thalassaemia, sickle cell disease or a blood cancer may need many transfusions. Over time some develop extra antibodies. For them, the blood bank may need more detailed matching, and finding suitable units can take longer. Ask the treating team whether this applies to your family member.
Who to ask
Take your questions about a specific transfusion to the treating doctor or the blood bank medical officer. At CION, the haematology team can explain why a transfusion has been advised and what the blood bank checks mean for your family.
Questions we are asked
Common questions about blood group compatibility
Which blood group is the universal donor?
For red cells, O negative is called the universal donor, because its cells carry no A, B or D marker. For plasma it is the other way round: AB plasma can be given to any group. Even so, hospitals test and match wherever there is time, and keep O negative for emergencies.
Can an O positive person donate to a B positive patient?
Usually yes, for red cells. O red cells carry no A or B marker, and a positive patient can receive positive or negative cells. The blood bank will still cross-match the unit against the patient's sample before it is given. The final decision always rests with the blood bank.
Can a positive group receive negative blood?
Yes. A positive patient can usually receive red cells from a negative donor of a suitable ABO group. The reverse is avoided where possible. A negative patient given positive cells can form antibodies against the D marker, which matters for future transfusions and, in women, for future pregnancies.
Does my blood group need to match for platelets?
A matching group is preferred, but it is less strict than for red cells. When stock is short, the blood bank may use another group. RhD type is considered carefully, especially for girls and women. If you are responding to a platelet request, call the blood bank and ask which groups they can accept.
Can my blood group change?
For almost everyone, no. It stays the same for life. The rare exception is after a stem cell transplant from a donor of a different group, when the patient's group slowly takes on the donor's. Some illnesses can also make grouping tests harder to read, which the laboratory will flag.
Why did the hospital retest my group when I already know it?
Because mistakes in identity and in old records are a known cause of serious transfusion reactions. Every hospital tests a fresh, labelled sample before a transfusion. It is a routine safety step and happens to every patient, however sure they are of their group.
What should we watch for during a transfusion?
Tell the nurse straight away if the patient develops a fever, shivering, a rash, itching, breathlessness, back or chest pain, or simply feels unwell. The nurse can pause the transfusion and check. Do not wait to see whether it settles on its own.
Does a blood group affect a person's health?
Your blood group matters mainly for transfusion, pregnancy and organ or stem cell donation. Claims that a group decides your diet or personality have no good evidence behind them. If you have a question about a health condition, ask your doctor rather than relying on your group.
Your Haematologist
Meet CION's haematologist. One specialist for your blood report and your plan.
Dr. Basudev Pokhrel reviews blood counts, transfusion needs and blood disorders, and works with the CION tumour board on blood cancers.
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Sources
- NHS — Blood groups
- NHS Blood and Transplant — Blood types
- American Red Cross — Blood types
- NHLBI — Blood transfusion
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
Rare Blood Groups and Bombay PhenotypeGroups the standard chart does not showWhat Happens to Donated BloodHow one donation becomes red cells, plasma and plateletsTransfusion Safety and Screening in IndiaThe tests every unit goes throughResponding to a Platelet Request on WhatsAppHow to help when a request reaches youTransfusion and Blood DonationThe full guide to transfusion and donation
Talk to us
Has a transfusion been advised for your family member?
Tell us what the reports say so far. Our haematology team will explain why blood has been advised and what to ask the treating team. One helpline serves every CION centre.