A titer test is a simple blood test that is used to detect the presence and amount of antibodies in a dog to determine if they have immunity from a given disease.
Titer tests are typically not covered by insurance, but represents money out-of-pocket well spent especially if your dog is above the age of 4 and has received all core vaccines already or is a pure breed.
If your dog is at least 4 years of age, regardless of breed, they have most probably received vaccinations for rabies, distemper, parvo and a bunch of others. Since vaccines have been designed to remain active and effective in the body for 7-15 years, it is extremely unlikely that he or she will need further vaccinations for the rest of their life. If your dog is 4+ years old and has core vaccines, ask for titer tests before administering any more.
If your dog is a pure breed, vaccinating deliberately and carefully becomes even more important. For example, take any litter of pure bred pups. Their parents have been vaccinated, their parents parents' have been vaccinated and their parents parents' parents' have been vaccinated and so on. At this point, it is probable that immunity is most likely inherited from their parents. Asking for titer tests when your dog is a puppy, although it may be more expensive up front, could save you and your dog from the complications of too many vaccines. If you want to learn more about the complications of too many vaccines, also called vaccinosis, please click here.
Unfortunately, most vets treat all pets with the "one size fits all" approach, which absolutely does not reflect how to optimize your dogs' health. Vaccines should not be administered if your dog is sick, period.
If they are chronically sick with an autoimmune disease, cancer, or has an adverse reaction to vaccines, they should absolutely not be vaccinated and your vet should give you a medical exemption letter, which simply states that whatever vaccine poses a threat to the health and well-being of your dog.