A Brief History of Blood Typing
For most of human history, blood transfusions were a mystery — and often fatal. Early 17th-century experiments by physicians like Richard Lower demonstrated that blood could be moved between animals, but human transfusions remained dangerous because doctors did not understand why some worked and others killed the patient.
The breakthrough came in 1901 when Austrian physician Karl Landsteiner discovered that human blood could be divided into distinct groups. By mixing blood from different donors and observing clumping (agglutination), he identified three types — A, B, and O. A fourth type, AB, was discovered in 1902 by his colleagues. Landsteiner received the Nobel Prize in Physiology or Medicine in 1930 for this work, which made safe transfusion medicine possible.
The Rh factor was identified in 1940, again largely by Landsteiner and Alexander Wiener, named after experiments with Rhesus monkeys. Understanding Rh incompatibility was critical for preventing hemolytic disease of the newborn — a condition where a Rh-negative mother's antibodies attack a Rh-positive fetus. Today, the ABO-Rh system forms the foundation of transfusion safety worldwide.
Understanding ABO and Rh
Red Cell Compatibility Chart
| Blood Type | Donate Red Cells To | Receive Red Cells From | World % |
|---|---|---|---|
| O− | All types | O− | ~7% |
| O+ | O+, A+, B+, AB+ | O−, O+ | ~38% |
| A− | A−, A+, AB−, AB+ | O−, A− | ~6% |
| A+ | A+, AB+ | O−, O+, A−, A+ | ~28% |
| B− | B−, B+, AB−, AB+ | O−, B− | ~2% |
| B+ | B+, AB+ | O−, O+, B−, B+ | ~9% |
| AB− | AB−, AB+ | O−, A−, B−, AB− | ~1% |
| AB+ | AB+ only | All types | ~3% |
Blood Type Distribution
- •O+ is the most common type globally (~38%), making O+ donors critically important for blood supplies worldwide.
- •AB− is the rarest type (~1%), but AB− donors are highly valued because their red cells can be given to any Rh-negative patient.
- •Distribution varies significantly by population: Type B is much more common in South and East Asian populations; Type O dominates in Indigenous American populations.
- •Blood banks constantly need donations from all types — rarity does not mean you are less needed; it often means the opposite.
Blood Type and Health Research
- 1.Research suggests that people with Type O blood may have slightly lower risk of heart disease and certain cancers, but the evidence is not conclusive.
- 2.Type A individuals may have a modestly higher risk of stomach cancer; Type B has been associated with slightly higher rates of pancreatic cancer in some studies.
- 3.During the COVID-19 pandemic, early studies suggested Type O individuals had somewhat lower susceptibility — later confirmed by larger genome-wide studies, though the protective effect is modest.
- 4.Rh-negative mothers carrying Rh-positive babies can develop anti-Rh antibodies (if untreated) that may attack future Rh+ pregnancies — a condition now prevented with Rh immunoglobulin (RhoGAM) injections.
- 5.Blood type "diets" (eating based on your ABO type) are not supported by scientific evidence. Blood type does not determine your optimal diet.
How to Use This Information
- 1
Understand the ABO system
Blood type is determined by antigens on red blood cells. Type A has A antigens, Type B has B antigens, Type AB has both, Type O has neither. Your body produces antibodies against antigens you don't have.
- 2
Understand the Rh factor
The Rh factor (+ or −) is a separate antigen. Rh+ means you have it; Rh− means you don't. This gives 8 blood types: A+, A−, B+, B−, AB+, AB−, O+, O−.
- 3
Know donation compatibility
O− is the universal red cell donor. AB+ is the universal recipient. For plasma, AB is the universal donor. Always confirm with a medical professional before any transfusion.
- 4
Check your blood type
Find your blood type from a prior blood test result, blood donation record, or a home blood typing kit. Ask your doctor if unsure.
- 5
Use the reference guide
Use our Blood Type reference tool to look up compatibility charts, distribution by population, and what each type means clinically.
Blood Type Guide
Explore the interactive tool →Frequently Asked Questions
What is the rarest blood type?
AB− is the rarest, found in roughly 1% of people. O+ is the most common (≈38% globally).
Does blood type affect health?
Research links some blood types to slightly different disease risk profiles, but the effect is small and lifestyle matters far more.
Can blood type change?
Blood type is genetic and does not change. Rare exceptions occur after bone marrow transplants.