Titers are blood tests that check immune status to vaccinations or diseases, one might have had in the past. If the titer is positive then one does not need to get the vaccination again as the immunity is adequate enough to fight the particular disease, if however, the titer is negative you may have to get the vaccination again get the vaccinations. Blood type A has A antibodies and anti-B antibodies hence it cannot accept type B or AB blood, but can accept A or O blood type. Similarly blood type B can accept B or O blood type, as blood type B has B antibodies and anti -A antibodies. Anti B titer is performed to measure the level of anti B titer in blood. There are different kinds of titers tests like the Hepatitis A titers, Hepatitis B titers, NMR titers, Rabies titers, etc.