Titer has become a very important and often controversial term in today’s veterinary world. No laboratory test in my memory has been more misunderstood, misinterpreted, misused, and downright maligned by owners and veterinarians alike. The most extreme example is the rabies vaccination. While this simple test determines if a dog has responded to vaccination and is immune to rabies virus, and can be allowed to travel to a rabies free country, it is not accepted as proof of immunity in the United States.
So why are dogs still being vaccinated frequently, when science does not support it? Why is the scientific test demonstrating immunity, the titer, disregarded or misunderstood by many?
A titer is a blood test that determines the level of antibodies (disease fighting proteins produced by the immune system) to a given disease-causing virus in the body. It is expressed as a dilution. This means that the antibody level is measured in the sample as it came from the dog, then diluted in half, then in half again, and so on until the antibody level cannot be detected. The titer is the lowest dilution of the blood sample in which antibodies can be measured. A high titer is one in which antibodies can be measured in a very dilute sample. We know that a dog is immune to a disease if he has a certain level of antibodies, and we use the expression “protective titer” to mean enough antibodies are present to fight off disease.
Sounds simple, doesn’t it? Either the dog has protective antibodies, or he doesn’t?
The answer is yes, and no.
Initially, after a dog is vaccinated, if he is tested and results indicate a protective titer, he should be protected for some time. Research published as long ago as 1998 estimates protection from distemper and parvovirus vaccines as lasting 9-15 years. Yes, years.
Aside from producing antibodies in response to vaccination, the immune system produces memory cells. These long-lived cells retain the information needed by the body to manufacture antibodies. Unfortunately, we have no easy way to measure them, but we know they are produced if antibodies are produced. And this is the key point you need to remember about titers – if a dog has titered at a protective level, he has been proven to be immunocompetent. His immune system is working properly, responding to the vaccine that was given, and producing antibodies and memory cells.
At this point, when you have proven that the dog’s immune system is competent, and has responded correctly to the vaccine given, YOU ARE DONE. There is no scientific need to re-titer. Most titers do not change significantly in less than three years. And, since memory cells persist for life, the normal dog’s immune system will be able to produce more antibodies in the face of disease exposure.
And this is the point where most veterinarians and owners lose their way when it comes to fully understanding titers.
There are three key points to remember:
- Repeating titers yearly is a waste of money
- Repeating titers every three years is not necessary
- Re-vaccinating a dog who has previously titered as protected, but now tests below the minimum is unnecessary
Yes, you do NOT need to vaccinate a dog if his titer falls from the protected to the low range – because he still has memory cells!
The typical dog whose titer falls below threshold is the healthy senior dog, who stays at home and has little exposure to any diseases. It would be a waste of his body’s energy to keep producing antibodies to viruses he was not being exposed to. So, his circulating antibody level falls. Should he be exposed to a virus, his immune system will begin to make antibodies with the information encoded in the memory cells. And he will be protected against the disease in question. (Note: I am speaking of a normal dog – dogs with immunosuppressive diseases or neoplasia may be at risk for contracting disease, and decisions regarding vaccination for them must be made on an individual basis.)
To reiterate – it is not necessary in most cases to re-vaccinate a dog because their titer fell below the laboratory’s protective level.
You may be asking now how you get your dog titered. Many veterinary laboratories offer titers. Costs vary greatly. I prefer a numerical value for the titer, rather than a protected/not protected result. Kansas State Veterinary Diagnostic Lab is the most utilized US laboratory for titers, and I prefer their program over any other test.
Many owners have heard of an in-house titer check kit. I do not encourage use of this kit, for several reasons. First, it relies on interpreting the colors of test and control dots. Lighting and visual acuity of the technician can influence results. Second, it provides only semi-quantitative results. Third, running the test takes about 30 minutes of technician time, during which they are unavailable to help with other hospital duties. This adds to the fee for the test, without any benefit to the owner. It’s much more efficient and cost-effective for a veterinarian to utilize KSU’s laboratory via your veterinarian, Healthy Dog Workshop, or others
So w
hen do you start using titers? If you have a puppy, check out my vaccination protocol. If you have an adult dog, you can run a titer at any time that is at least four weeks after a vaccination, and then follow my vaccination protocol, providing the dog is normal. Decisions about vaccinating dogs with chronic disease or conditions should be made on a case by case basis, with your veterinarian’s input.
Please read my follow up on this topic, where I reveal the results of titer testing dogs that have not been vaccinated for distemper and parvovirus.