Glossary
Vaccine titer
A blood test that measures antibodies to a germ, sometimes used to judge whether a cat is protected after vaccination.
Also called: titer test, antibody titer, vaccine titre, serology
A titer is a measure of the antibodies in a blood sample. After a vaccine or an infection the body makes antibodies, and a titer test shows how many are present against one disease. Some owners ask for a titer to decide whether a booster is needed.
The result is only as useful as the link between antibodies and real protection. For feline panleukopenia, a good titer is a fair sign of protection. For herpesvirus and calicivirus, antibody levels do not predict protection well, because other parts of the immune system matter. Feline leukemia titers do not show immunity either. A low result does not always mean a cat is unprotected, and a result can be hard to interpret in a kitten that still carries antibodies from its mother.
Titer tests are also used to diagnose past infection, such as with coronavirus. In that case a positive result only shows exposure and does not mean the cat is sick. Rabies titers are sometimes required for international travel, though they do not replace the legal vaccination in most places. Ask your vet whether a titer will help in your cat's case, what a result would change, and how the clinic reads it.
Last reviewed November 7, 2026