Understanding Rh-Negative Blood Type: Definition & Facts

Rh-negative is when blood lacks the Rh antigen (or Rhesus factor) in the body. Antigens induce an immune response in the body. Blood is classified in four categories--A, B, O and AB--and is also labeled as Rh-positive (the Rh factor is present) or Rh-negative (the Rh factor is absent).

Definition

• The Rh (Rhesus) factor is an antigen (protein) on the surface of red blood cells. The term Rhesus factor comes from the Rhesus monkey, a breed used in research that led to the discovery of this certain antigen in 1940.

Compatibility

• Rhesus-positive individuals can receive either Rh-positive or negative blood; however, Rh-negative individuals can only receive Rh-negative blood.

Importance

• Rhesus factor is most important during pregnancy and blood transfusions. If the blood of a Rh-negative mother and a Rh-positive baby mix, the mother's antibodies will attack the fetal red blood cells. The condition known as hemolytic disease or hemolytic anemia can be serious, even causing death in a fetus or newborn.

Distribution

• Most of the worldwide population (approximately 85 percent) is Rh-positive, although it varies by race, with that range reaching 90 to 95 percent for African-Americans.

Misconception

• There are many bizarre theories about people who are Rh-negative. One is that they portray reptilian traits like having a lower than normal blood pressure and pulse rate.