Anti A titre is antibody A titre test is to measure the level of antibody A in the blood. It is performed to confirm ABO Incompatibility and also during and after the treatment of ABO Incompatibility. This test measures the amount of antibody in a person’s blood. The amount of antibodies determines the strength of the body’s immune system. The immune system produces antibodies to kill invading microorganisms before they can cause an infection. Invading microorganisms are known as pathogens. Pathogens have markers on them known as antigens, which antibodies find and bind to.