Antibody titers are sometimes needed to diagnose disease. Antibody titers reflect the level of antibody that the pet has made in response to exposure to a certain infectious organism. The titer is determined by sequentially diluting the serum and testing it against the organism in question. The more dilute the serum when it stops producing a positive reaction, the higher the concentration of antibodies present in the blood. Titers give support to a diagnosis, allowing more targeted treatment and more specific prognostic information, as well as identifying zoonotic disease (diseases transmissible between animals and humans).