What is the universal blood donor blood type?

O negative (O-) is the universal blood donor for red blood cells. It can be given to patients of any blood type in emergency situations when there is no time to test the patient's blood type. O positive (O+) is the most common blood type and can donate to all positive blood types.

What blood types are compatible for transfusion?

For red blood cell transfusions: O- can donate to everyone. O+ can donate to A+, B+, AB+, O+. A- can donate to A+, A-, AB+, AB-. A+ can donate to A+ and AB+. B- can donate to B+, B-, AB+, AB-. B+ can donate to B+ and AB+. AB- can donate to AB+ and AB-. AB+ can only donate to AB+.

What is Rh factor incompatibility in pregnancy?

Rh incompatibility occurs when an Rh-negative mother carries an Rh-positive baby. The mother's immune system may produce antibodies against the baby's red blood cells, which can cause haemolytic disease of the newborn (HDN). This is managed with Rh immunoglobulin (RhIg/anti-D) injections during pregnancy and after delivery.

Can two O positive parents have a different blood type child?

No. Two O positive parents can only have O positive or O negative children, as both parents can only pass on the O allele. They cannot produce A or B antigens. However, if both parents carry hidden O alleles, the child's Rh factor can vary.

What blood type is the universal recipient?

AB positive (AB+) is the universal recipient for red blood cells. People with AB+ blood type can receive blood from any of the 8 blood types. However, for plasma donations, AB is the universal donor.

Blood Type Compatibility Calculator | Transfusion, Pregnancy & Relationship

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Content reviewed against American Red Cross blood type compatibility guidelines and WHO blood safety standards. Last updated: July 2026.

Reference

Complete Transfusion Compatibility Chart

For red blood cell transfusions. Rows = Donor blood type. Columns = Recipient blood type.

✅ = Compatible | — = Not compatible | ✅ in red = You (if blood type selected)

Population Data

Blood Type Frequency

Approximate prevalence in the general population (varies by ethnicity and region).

O+

~38% of population

Most common. Can donate to O+, A+, B+, AB+

A+

~34% of population

Second most common. Can donate to A+ and AB+

B+

~9% of population

Can donate to B+ and AB+

AB+

~3% of population

Universal recipient. Can receive from all 8 types

O−

~7% of population

Universal donor. Can give to all 8 blood types

A−

~6% of population

Can donate to A+, A−, AB+, AB−

B−

~2% of population

Can donate to B+, B−, AB+, AB−

AB−

~0.6% of population

Rarest type. Universal plasma donor

What Is Blood Type Compatibility?

Blood type compatibility refers to whether two people's blood types can safely interact — most critically for blood transfusions, organ transplants, and pregnancy. Blood type is determined by antigens on red blood cells (A, B, or neither) and the Rh factor (positive or negative). Incompatible blood triggers an immune reaction that can be fatal.

The ABO and Rh systems are the two most important blood group systems in medicine. ABO incompatibility can cause a severe, life-threatening haemolytic transfusion reaction. Rh incompatibility in pregnancy, known as haemolytic disease of the newborn (HDN), can cause serious complications for the baby if untreated.

The ABO Blood Type System

The ABO system classifies blood into four groups based on the presence or absence of A and B antigens on the surface of red blood cells:

Type A — has A antigens. Has anti-B antibodies. Can receive A and O blood.
Type B — has B antigens. Has anti-A antibodies. Can receive B and O blood.
Type AB — has both A and B antigens. No ABO antibodies. Universal recipient.
Type O — has no ABO antigens. Has both anti-A and anti-B antibodies. Universal donor for red cells.

The Rh Factor

The Rh factor is a protein (antigen) on red blood cells. If you have it, you are Rh positive (+). If not, you are Rh negative (-). In transfusions, Rh-negative patients should generally receive Rh-negative blood. In pregnancy, Rh incompatibility between a Rh-negative mother and Rh-positive baby requires medical management.

Universal Donor and Universal Recipient

O negative (O−) is the universal donor for red blood cells — it can be given to patients of any blood type and is used in emergencies before blood type testing. O− blood is always in short supply because it is used in emergencies and is relatively rare (only 7% of the population).

AB positive (AB+) is the universal recipient for red blood cells — people with AB+ can receive from any donor. However, AB is the universal donor for plasma.

Blood Type Compatibility in Pregnancy

Rh incompatibility occurs when an Rh-negative mother carries an Rh-positive baby (inherited from the father). During delivery or bleeding in pregnancy, fetal red blood cells can enter the mother's bloodstream. The mother's immune system may produce anti-Rh antibodies, which in future pregnancies can cross the placenta and attack the baby's red blood cells.

This is prevented with Rh immunoglobulin (RhIg/anti-D) injections given to Rh-negative mothers at 28 weeks of pregnancy and within 72 hours of delivery. This is now routine care in the UK, US, Australia, and Canada.

Can Blood Type Predict Relationship Compatibility?

In Japan and South Korea, blood type personality theory (ketsueki-gata) is a popular cultural belief — similar to astrology — suggesting blood type influences personality and relationship compatibility. While this is not scientifically validated, it is a fun and widely-shared cultural phenomenon.

Scientifically, blood type has no proven effect on personality or relationship success. However, blood type compatibility does matter practically for couples planning to have children, as Rh incompatibility requires medical management in pregnancy.

⚕️ Medical Disclaimer: Blood type compatibility information in this tool is for educational purposes only. Never make medical decisions based on this tool. All transfusions, transplants, and pregnancy management must be conducted under qualified medical supervision.

Frequently Asked Questions

O negative (O−) is the universal blood donor for red blood cells. It can be given to patients of any blood type in emergencies. O positive (O+) is the most common blood type and can donate to all positive blood types (A+, B+, AB+, O+).

O− can donate to all 8 types. O+ can donate to A+, B+, AB+, O+. A− to A+, A−, AB+, AB−. A+ to A+ and AB+. B− to B+, B−, AB+, AB−. B+ to B+ and AB+. AB− to AB+ and AB−. AB+ only to AB+. For receiving: AB+ can receive from all types.

Rh incompatibility occurs when an Rh-negative mother carries an Rh-positive baby. The mother may produce antibodies against the baby's red blood cells, causing haemolytic disease of the newborn in future pregnancies. This is prevented with Rh immunoglobulin (anti-D) injections during pregnancy and after delivery.

AB negative (AB−) is the rarest blood type, found in approximately 0.6% of the population. AB positive (AB+) is the universal recipient for red blood cells. O negative (O−), the universal donor, is found in about 7% of the population.

Two O positive parents can only have O positive or O negative children. They cannot produce A or B antigens as both parents can only pass the O allele. The child may be O− if both parents carry the recessive Rh-negative allele.

AB positive (AB+) is the universal recipient for red blood cells — people with AB+ can receive from all 8 blood types. However, for plasma donations, AB is the universal donor. AB+ people are especially encouraged to donate platelets rather than whole blood.

Yes. Research has linked blood type to varying risks of certain conditions. Type A may have slightly higher risk of heart disease and stomach cancer. Type O appears to have some protection against heart disease but higher risk of stomach ulcers. These are statistical associations across large populations, not certainties for individuals.

Blood type is inherited from both parents. Each parent passes one ABO allele (A, B, or O) and one Rh allele. A and B are dominant over O. If you inherit A from one parent and B from the other, you become AB. If you inherit O from both, you become O. Rh positive is dominant over Rh negative.

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