Titer testing in cats

Want to avoid over-vaccinating your cat? Titer testing is a viable alternative to annual booster shots.

Jeannie recently adopted a three-year-old cat from her local shelter. Determined to give her new friend a healthy life, she decided not to have him vaccinated every year. She’d heard that vaccine titer testing was a good alternative to annual boosters, so she found a veterinarian who offers this option and asked him for more information.

Compelling evidence implicates vaccines in triggering various immune-mediated and other chronic disorders (vaccinosis). In cats, for example, aggressive tumors called fibrosarcomas can occasionally arise at the site of vaccination. While some of these problems have been traced to contaminated or poorly attenuated batches of vaccine that revert to virulence, others apparently reflect a genetic predisposition in an animal to react adversely when given the single (monovalent) or multiple antigen “combo” (polyvalent) products routinely administered to animals. Certain susceptible breeds or families of animal appear to be at increased risk for severe and lingering adverse vaccine reactions.

What is titer testing?

Titer testing for a particular infectious agent measures the presence and level of antibodies in an animal’s blood. These antibodies reflect the combination of any natural exposure and vaccination, and were created when the animal’s immune system responded to the antigens introduced into his body.

The presence of a measurable serum antibody titer indicates the presence of “immune memory”, and signifies protection from disease. Titers do not distinguish between immunity generated by vaccination and/or by exposure to the disease, although the magnitude of immunity produced just by vaccination is usually lower. When an adequate immune memory has already been established, there is little reason to introduce unnecessary antigen, adjuvant and preservatives by administering booster vaccines. If titer levels are adequate, your cat has protection against future exposure to the infectious agent, and revaccination is not needed.

By measuring titers every three years, or more often if desired, you can determine whether your cat’s circulating immune response has fallen below levels of adequate “immune memory”. In that event, an appropriate vaccine booster can be administered.

A “motion picture that plays for years”

Some veterinarians have challenged the validity of using vaccine titer testing to assess whether individual animals are protected against common, clinically important infectious diseases. With all due respect, this represents a misunderstanding of what has been called the “fallacy of titer testing”, because research has shown that once an animal’s titer stabilizes, it is likely to remain constant for many years. It is often said that the antibody level detected by a titer test is “only a snapshot in time”. That’s simply not true — it is more like a “motion picture that plays for years”. A cat with an adequate antibody level doesn’t need to be revaccinated, especially when the vaccine could cause an adverse reaction (hypersensitivity disorder). You should avoid vaccinating cats that are already protected.

Positive versus negative results

A positive titer test result is fairly straightforward, but a negative titer test result is more difficult to interpret, because it’s is not the same thing as a zero titer and doesn’t necessarily mean the cat is unprotected. A negative result usually means the titer has failed to reach the threshold of providing protective immunity. For the clinically important panleukopenia in cats, a negative or zero antibody titer indicates the animal is likely to be unprotected against feline panleukopenia virus.

High efficacy

More than a decade of experience with vaccine titer testing demonstrates this procedure is effective. Published studies in refereed journals show that 90% to 98% of cats that have been properly vaccinated develop good measurable antibody titers to the infectious agent being measured. Using titer testing as a means to assess vaccine-induced protection means you can avoid giving your cat needless and unwise booster vaccinations. So next time you set up a veterinary appointment for your cat, do as Jeannie did and ask if they offer titer testing.

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Dr. Jean Dodds received her veterinary degree in 1964 from the Ontario Veterinary College. In 1986, she established Hemopet, the first non-profit national blood bank program for animals. Today, Hemopet also runs Hemolife, an international veterinary specialty diagnostics service. Dr. Dodds has been a member of many committees on hematology, animal models of human disease and veterinary medicine. She received the Holistic Veterinarian of the Year Award from the AHVMA in 1994, has served two terms on the AHVMA’s Board of Directors, chairs their Communications Committee, and currently serves on the Board of the AHVMF, as well as its Research Grant and Editorial Committees.