This classification is not merely administrative. When a blood transfusion is required, doctors analyze a patient’s RhD antigen status to confirm compatibility. “When antigens come into contact with substances that are unfamiliar to your body, such as certain bacteria, they trigger a response from your immune system. The same type of response can occur during a blood transfusion if your donor’s blood type doesn’t match with yours. In that case, your blood cells could clump and cause potentially fatal complications,” explained Dr. Guggenheim from the Abramson Cancer Center Cherry Hill.
Testing for blood type involves drawing a blood sample and mixing it with antibodies against type A and type B blood, then observing whether the cells clump together. Type O blood is notable in that it can be given to individuals of any blood type group, since it contains both anti-A and anti-B antibodies.
The ABO system: over a century of blood classification
The ABO blood group system was established by Dr. Karl Landsteiner, whose work laid the foundation for safe blood transfusions. Blood type is genetically inherited and determined by the presence of specific antigens on red blood cells, as well as the Rh factor. Together, these markers define eight common blood type variants (A+, A−, B+, B−, AB+, AB−, O+, O−).
Types A and B: a statistically higher risk of heart attack and dangerous clots
People with type A or type B blood face measurably elevated cardiovascular risks, according to a study published in the American Heart Association journal. Individuals in these two groups had a combined 8% greater risk of heart attack and a 10% greater risk of heart failure compared to those with other blood types.
The circulatory risks extend beyond the heart itself. The same research found that people in the A or B groups had a 51% greater chance of developing deep vein thrombosis — dangerous blood clots that typically form in the legs — and a 47% higher risk of pulmonary embolisms, clots that travel to the lungs and can be life-threatening.
These figures represent statistical associations observed across study populations, not a guarantee that any individual with type A or B blood will develop these conditions.
AB blood type, the rarest group, carries the highest dementia-linked memory risk
The AB blood type is the least common in the United States, accounting for roughly 4% of the American population. Research suggests this group also faces a disproportionate risk when it comes to cognitive health in later life.
One study found that individuals with AB blood were 82% more likely to develop memory and cognitive issues linked to dementia than people with any other blood type. The nature of the biological mechanism behind this association is not detailed in the available research findings.
