Blood Type Compatibility Calculator

Blood type compatibility is critical for safe blood transfusions and organ transplants. Giving the wrong blood type can trigger a life-threatening immune reaction, so doctors always match blood types before any transfusion.

The ABO System

Human blood is classified into four main types based on antigens on red blood cells:

• Type A — has A antigens, makes anti-B antibodies
• Type B — has B antigens, makes anti-A antibodies
• Type AB — has both antigens, makes no antibodies (universal recipient for red cells)
• Type O — has no antigens, makes both anti-A and anti-B antibodies (universal donor for red cells)

The Rh Factor

In addition to ABO type, blood is either Rh-positive (+) or Rh-negative (−) based on the Rh antigen. This creates 8 common blood types: A+, A−, B+, B−, AB+, AB−, O+, O−.

Rh-negative patients should generally receive Rh-negative blood, especially women of childbearing age, to prevent sensitization.

Transfusion Compatibility Rules

• O− (Rh negative): Universal donor for red blood cells. Can give to anyone. Can only receive O−.
• AB+ (AB positive): Universal recipient. Can receive from anyone. Can only donate to AB+.
• O+: Can donate to all positive types (A+, B+, AB+, O+). Can receive from O+ and O−.
• A+: Can receive from A+, A−, O+, O−.
• B+: Can receive from B+, B−, O+, O−.
• AB+: Can receive from all types.

Plasma Compatibility (Reverse)

Plasma compatibility works the opposite way — AB is the universal plasma donor, and O is the universal plasma recipient.

Important Note

This tool is for educational reference only. Medical professionals perform cross-matching tests before any real transfusion, which checks for additional antibody incompatibilities beyond just ABO and Rh type. Always follow your doctor’s guidance.