The antibody titer detects and measures the amount of antibodies in the blood.
Antibodies are proteins made by the immune system.
These antibodies are made to attack a real or imagined threat. For example, antibodies may be made in some cases to attack bacteria causing an infection. In other cases, however, antibodies may be made to attack a person's own body. One common function of the antibody titer is to detect antibodies that the body has made to fight off a certain disease. Sometimes this is done to check whether a person has gotten a vaccine against a disease.