Specific Titer Tests
You may wonder how we know whether or not a certain level of antibodies measured in the blood mean that individual is protected against that disease. The answer is that the only way to know is through challenge testing. This means that we have to measure antibody levels in a number of individuals with a variety of different titers, then try to infect them with the specific disease we are studying and see which ones get sick and which don’t. This is how cutoff levels for antibody titers have been determined for CDV, CPV, Rabies, and other canine and feline vaccine-preventable disease.
This kind of challenge testing may only be accurate for a specific titer testing method. So if two different laboratories use two different types of titer test, the titer level that is protective will be different, and both would need to do challenge testing to figure out what titer level is protective for the specific test method they each use.
Above is an excerpt from. http://skeptvet.com/Blog/2014/12/antibody-titer-testing-as-a-guide-for-vaccination-in-dogs-and-cats/ click on link for full article .
