Q: What are the eight common blood groups?

The eight commonly recognized ABO/RhD blood groups are O+, O-, A+, A-, B+, B-, AB+, and AB-.

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A simple guide to A+, A−, B+, B−, AB+, AB−, O+ and O− blood groups, red blood cell compatibility, and what it means when someone needs blood.

Blood groups can seem complicated at first. You may have heard that O-negative is a universal donor, that AB-positive can receive blood from all common blood groups, or that your blood type determines who you can donate to.

But what does all of this actually mean?

Understanding blood group compatibility is important for both donors and people looking for blood. It can help you understand why a particular blood group may be requested and why blood banks and hospitals carefully test and match blood before a transfusion.

This guide explains the basics in simple terms.

Important: The compatibility information in this article is for general education and refers primarily to red blood cell compatibility. A blood-group match does not by itself guarantee that a transfusion is safe. The treating hospital or authorized blood centre must perform the required testing and cross-matching and make the final transfusion decision.

What Are Blood Groups?

Your blood group is determined by specific markers, called antigens, on the surface of your red blood cells.

The two systems most commonly used to describe the blood types we talk about every day are:

ABO
Rh (Rhesus), particularly RhD

Combining these systems gives the eight common blood groups:

ABO Group	Rh Type	Blood Group
O	Positive	O+
O	Negative	O−
A	Positive	A+
A	Negative	A−
B	Positive	B+
B	Negative	B−
AB	Positive	AB+
AB	Negative	AB−

The ABO system is based on whether your red blood cells carry A antigen, B antigen, both, or neither. The RhD system is based mainly on whether the RhD antigen is present.

Understanding the ABO Blood Groups

There are four main ABO groups:

Blood Group A

People with group A blood have A antigens on their red blood cells.

Their plasma generally contains anti-B antibodies.

Blood Group B

People with group B blood have B antigens on their red blood cells.

Their plasma generally contains anti-A antibodies.

Blood Group AB

People with group AB blood have both A and B antigens on their red blood cells.

Their plasma generally does not contain anti-A or anti-B antibodies.

Blood Group O

People with group O blood do not have A or B antigens on their red blood cells.

Their plasma generally contains both anti-A and anti-B antibodies.

These antigen-and-antibody differences are one of the main reasons blood-group compatibility matters during transfusion.

What Does the Positive or Negative Sign Mean?

The + or − in a blood group refers to the RhD factor.

Rh-positive (+)

A person whose red blood cells have the RhD antigen is generally described as Rh-positive.

Rh-negative (−)

A person whose red blood cells do not have the RhD antigen is generally described as Rh-negative.

For example:

A+ = A group + RhD positive
A− = A group + RhD negative
O+ = O group + RhD positive
O− = O group + RhD negative

RhD compatibility is particularly important when selecting red blood cells for transfusion.

Why Does Blood Group Compatibility Matter?

When red blood cells from a donor are transfused into another person, the recipient's immune system can recognize certain donor red-cell antigens as foreign.

If incompatible blood is transfused, antibodies can react against the donor red blood cells. This can cause a serious transfusion reaction.

That's why hospitals and blood centres do not simply look at someone's blood group and immediately give them blood.

They use appropriate pre-transfusion testing and cross-matching to select compatible blood. Indian transfusion guidance states that ABO-identical blood is preferred whenever possible and that compatible alternatives may be used when group-specific blood is unavailable.

Red Blood Cell Compatibility

When people talk about blood groups being compatible, they are often talking about red blood cells.

Red blood cells contain the antigens that are important for ABO and RhD matching.

For general red-cell compatibility:

O red cells can generally be given to O, A, B and AB recipients when Rh requirements are also satisfied.
A red cells can generally be given to A and AB recipients when Rh requirements are satisfied.
B red cells can generally be given to B and AB recipients when Rh requirements are satisfied.
AB red cells can generally be given to AB recipients.

The RhD factor adds another layer of compatibility.

Who Can Donate Red Blood Cells to Which Blood Group?

Here is the standard ABO/RhD red blood cell compatibility guide.

Donor Blood Group	Can Generally Donate Red Blood Cells To
O−	O−, O+, A−, A+, B−, B+, AB−, AB+
O+	O+, A+, B+, AB+
A−	A−, A+, AB−, AB+
A+	A+, AB+
B−	B−, B+, AB−, AB+
B+	B+, AB+
AB−	AB−, AB+
AB+	AB+

This is the simplified ABO/RhD compatibility pattern for red blood cells. Actual transfusion decisions require laboratory testing and clinical assessment.

Who Can Receive Red Blood Cells From Which Blood Group?

Looking at compatibility from the recipient's perspective:

Recipient Blood Group	Can Generally Receive Red Blood Cells From
O−	O−
O+	O−, O+
A−	A−, O−
A+	A+, A−, O+, O−
B−	B−, O−
B+	B+, B−, O+, O−
AB−	AB−, A−, B−, O−
AB+	AB+, AB−, A+, A−, B+, B−, O+, O−

Whenever possible, patients generally receive red blood cells that are identical in ABO and RhD type. Other compatible options may be used in particular circumstances, including emergencies or shortages, under the direction of the transfusion service.

An Easy Way to Understand the Pattern

You don't have to memorize the entire table.

Think about the ABO system first.

O

O red cells can generally be given to:

O → O, A, B, AB

A

A red cells can generally be given to:

A → A, AB

B

B red cells can generally be given to:

B → B, AB

AB

AB red cells can generally be given to:

AB → AB

Then consider the RhD factor.

For example:

O+ can generally donate red cells to: O+, A+, B+, AB+

while:

O− can generally donate red cells to all eight common ABO/RhD groups.

Why Is O-Negative Called the Universal Red Cell Donor?

O-negative is commonly called the universal red blood cell donor because O-negative red cells lack A, B and RhD antigens.

This makes O-negative red cells suitable for patients of different ABO/RhD groups in situations where O-negative red cells are required or appropriate, including certain emergencies.

However, there is an important distinction:

Universal donor does not mean "the only blood group that matters."

Blood centres need donors from all blood groups.

A patient who is A-positive, for example, may normally need A-positive or another appropriate compatible blood product. Having a reliable supply of A-positive blood is therefore important.

Indian transfusion guidance also states that ABO-identical blood should be preferred whenever possible, with alternate compatible blood used when necessary.

Why Is AB-Positive Called the Universal Red Cell Recipient?

AB-positive is commonly described as the universal red blood cell recipient.

An AB-positive person has both A and B antigens and is RhD-positive, meaning that, in the standard ABO/RhD compatibility framework, they can generally receive red blood cells from all eight common blood groups.

That includes:

O−
O+
A−
A+
B−
B+
AB−
AB+

But this does not mean that every AB-positive patient can automatically receive any available blood without testing.

The hospital or blood bank still performs the required compatibility testing.

What Happens If the Exact Blood Group Isn't Available?

Ideally, patients receive blood that matches their ABO and RhD type.

However, real-world situations can be more complicated.

A hospital may sometimes need to use another ABO-compatible blood group when the patient's exact group is unavailable, particularly in urgent situations.

Indian transfusion guidance specifically describes the use of alternate ABO-compatible blood when group-specific blood is unavailable.

The decision is made by the blood bank/transfusion service based on the patient's situation and available blood.

This is why a person should never attempt to determine their own transfusion compatibility using an online table.

What Is Cross-Matching?

Blood-group compatibility is only one part of transfusion safety.

Before a transfusion, the laboratory may perform tests to determine whether the donor's red cells are compatible with the recipient.

This process is commonly referred to as cross-matching.

Cross-matching helps identify incompatibilities that may not be obvious from simply looking at the ABO and RhD blood groups.

Indian transfusion guidance notes that compatibility testing can detect incompatibilities involving different types of antibodies and requires appropriate testing before blood is issued.

Blood Group Compatibility Is More Than A, B, AB and O

ABO and RhD are extremely important, but they are not the only blood-group systems that exist.

There are many other red blood cell antigens.

Some patients may have antibodies against other antigens because of previous transfusions, pregnancy, or other circumstances.

This is one reason transfusion services may need to perform additional antibody screening and select specially matched blood in some cases.

For example, patients who require repeated transfusions may need additional antigen matching depending on their medical circumstances.

So:

ABO/RhD compatibility is a useful starting point — not the complete transfusion decision.

What About Plasma?

This is an important distinction.

Red blood cell compatibility and plasma compatibility are not the same.

Red blood cells carry A, B and RhD antigens.

Plasma contains antibodies.

Because of this, plasma compatibility follows a different pattern.

For example, AB plasma can generally be given to patients of any ABO group, which is why AB is commonly described as the universal plasma donor.

For plasma:

Recipient ABO Group	Compatible Plasma Donor Groups
O	O, A, B, AB
A	A, AB
B	B, AB
AB	AB

This is why Lifia should always specify whether a compatibility table refers to red blood cells, plasma, or another blood component.

What About Platelets?

Platelets have their own compatibility considerations.

ABO-identical platelets are generally preferred where possible, but platelet transfusion decisions can depend on availability and the patient's clinical circumstances.

This is another reason why a simple statement such as:

"Blood group X can always be given to blood group Y"

is too broad for a medical platform.

Compatibility depends on the blood component, laboratory testing, and clinical situation.

Your Blood Group Doesn't Make Your Donation More or Less Valuable

One of the biggest misconceptions about blood donation is that only certain blood groups are valuable.

That's not true.

Every blood group is important.

Hospitals and blood centres need a reliable supply of different blood groups because patients have different blood types and different transfusion requirements.

O-negative donors are especially valuable in situations where O-negative red cells are required, but A+, B+, O+, AB+, and the negative blood groups are all needed as well.

What If I Don't Know My Blood Group?

That's completely okay.

You don't need to know your blood group before deciding that you want to become a donor.

Your blood group can be determined through testing as part of the blood donation process.

So don't let:

"I don't know my blood group."

stop you from considering blood donation.

Can Blood Group Change?

Your blood group is genetically determined and normally remains the same throughout your life.

However, there are unusual medical circumstances in which blood-group testing can become more complicated.

For everyday purposes, the blood group recorded through appropriate laboratory testing is what matters for transfusion.

If there is any uncertainty or discrepancy, the blood bank will investigate before selecting blood for transfusion.

Why Blood Banks Take Compatibility Seriously

A blood transfusion is a medical procedure.

Blood banks and hospitals therefore follow controlled processes to ensure that the right blood product is provided to the right patient.

These processes can include:

Identifying the patient.
Testing the patient's blood group.
Screening for clinically significant antibodies.
Selecting an appropriate blood component.
Testing or cross-matching the donor unit as required.
Verifying the blood unit before issue.
Monitoring the patient during transfusion.

Indian transfusion guidance emphasizes checking the selected unit, confirming ABO and RhD information, and issuing blood through the blood bank/blood centre with the appropriate compatibility documentation.

Blood Group Compatibility at a Glance

Red Blood Cells

Blood Group	Can Generally Donate Red Cells To	Can Generally Receive Red Cells From
O−	All 8 common groups	O−
O+	O+, A+, B+, AB+	O−, O+
A−	A−, A+, AB−, AB+	A−, O−
A+	A+, AB+	A+, A−, O+, O−
B−	B−, B+, AB−, AB+	B−, O−
B+	B+, AB+	B+, B−, O+, O−
AB−	AB−, AB+	AB−, A−, B−, O−
AB+	AB+	All 8 common groups

A Simple Example

Imagine a patient with A-positive blood needs red blood cells.

Based on standard ABO/RhD compatibility, compatible donor red-cell groups can include:

A+
A−
O+
O−

But the hospital does not simply search for one of these blood groups and transfuse it.

The blood bank performs the required testing and selects an appropriate unit.

Now imagine another patient with O-negative blood.

Their compatible red-cell donor group is generally:

O−

This is one reason maintaining an adequate supply of O-negative blood is particularly important.

Why Lifia Uses Blood Groups to Help Connect Donors and Requests

Lifia is designed to help people find potential blood donors nearby through a structured, privacy-first process.

A blood request can include a required blood group, allowing donors with the relevant blood group to discover requests that may be relevant to them.

However, there is an important distinction:

Lifia can help connect people based on blood-group information, but Lifia does not determine final transfusion compatibility.

The treating hospital or blood bank remains responsible for:

Confirming the patient's blood group
Testing the donor blood
Performing compatibility testing
Determining whether the blood can be safely transfused

This keeps Lifia's role clear:

Lifia connects people. Qualified medical professionals make transfusion decisions.

Frequently Asked Questions

What are the eight common blood groups?

The eight commonly recognized ABO/RhD blood groups are O+, O−, A+, A−, B+, B−, AB+, and AB−.

Which blood group is the universal red blood cell donor?

O-negative is commonly called the universal red blood cell donor because O-negative red cells lack A, B and RhD antigens.

Which blood group is the universal red blood cell recipient?

AB-positive is commonly called the universal red blood cell recipient because, within the standard ABO/RhD system, AB-positive recipients can generally receive red blood cells from all eight common blood groups.

Can O-positive donate to A-positive?

Yes. O-positive red blood cells can generally be donated to A-positive recipients.

Can A-positive donate to O-positive?

No. A-positive red blood cells are generally not compatible with an O-positive recipient.

Can O-negative donate to everyone?

O-negative red blood cells are commonly considered universally compatible across the eight common ABO/RhD groups, particularly in appropriate emergency settings. However, hospitals still follow transfusion protocols and perform required testing.

Can AB-positive donate to everyone?

No. AB-positive red blood cells can generally be donated only to AB-positive recipients. AB-positive is commonly known as the universal red-cell recipient, not the universal red-cell donor.

Can someone with AB-positive blood receive O-negative blood?

Yes, O-negative red blood cells are generally compatible with an AB-positive recipient.

Does blood group compatibility apply to plasma?

No. Plasma compatibility is different from red blood cell compatibility. AB plasma, for example, can generally be given to recipients of any ABO group.

Do I need to know my blood group before donating?

No. You can register as a donor even if you don't know your blood group.

Is blood-group matching enough before a transfusion?

No. ABO/RhD compatibility is only part of the process. Hospitals and blood banks perform appropriate testing and cross-matching before transfusion.

Can a person's blood group change?

Normally, your blood group remains the same throughout life. Rare medical circumstances can make blood-group testing more complex, but these are handled by medical professionals and transfusion laboratories.

Why does Lifia ask for my blood group?

Blood group is useful for helping identify potentially relevant blood requests. However, a Lifia match is not a medical compatibility guarantee. Final compatibility is determined by the treating hospital or blood bank.

The Most Important Thing to Remember

You don't need to memorize every compatibility rule.

Remember these basics:

O− — Often called the universal red-cell donor.
AB+ — Often called the universal red-cell recipient.
A — Red cells generally go to A and AB recipients when Rh-compatible.
B — Red cells generally go to B and AB recipients when Rh-compatible.
O — Red cells generally go to O, A, B and AB recipients when Rh-compatible.
AB — Red cells generally go to AB recipients when Rh-compatible.

And most importantly:

A blood-group match is not a substitute for medical testing.

Thinking About Becoming a Donor?

Your blood group doesn't need to be rare to matter.

Hospitals and blood centres need donors across different blood groups to maintain a reliable blood supply.

If you're considering becoming a donor, learn about the eligibility requirements and let the blood centre determine whether you're able to donate.

Register as a Donor · Find Blood

Medical & Safety Disclaimer

This article is provided by Lifia for general educational and informational purposes. It is not medical advice and should not be used to determine whether an individual is medically eligible to donate blood or whether a particular donor is suitable for a specific patient.

The blood-group compatibility information in this article is a simplified educational guide focused primarily on red blood cell ABO/RhD compatibility. Actual transfusion decisions require appropriate laboratory testing, antibody screening, cross-matching, clinical assessment, and the judgment of qualified medical professionals.

Lifia does not guarantee that a donor listed on the platform is medically eligible to donate or that a donor is transfusion-compatible with a particular patient.

If you need blood or are considering a blood transfusion, follow the instructions of the treating hospital, blood bank, or qualified healthcare professional.

Sources & Further Reading

Directorate General of Health Services (DGHS), Ministry of Health & Family Welfare, Government of India — Transfusion Medicine Technical Manual and Blood Transfusion Services guidance.
National Blood Transfusion Council (NBTC), Government of India.
Australian Red Cross Lifeblood — Blood group and component compatibility resources.

Content review: September 2026

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