[Beamers Mom]

From this site:

TITER TEST



Understanding titer tests
The term “titer” refers to the strength or concentration of a substance in a solution. When testing vaccine titers in dogs, a veterinarian takes a blood sample from a dog and has the blood tested for the presence and strength of the dog’s immunological response to a viral disease. If the dog demonstrates satisfactory levels of vaccine titers, the dog is considered sufficiently immune to the disease, or possessing good “immunologic memory,” and not in need of further vaccination against the disease at that time.