How come if I test my saliva and then my urine they are different?

It is the kidneys that buffer the metabolic acids and thus urine gives us the best indicator of our acid load. Saliva is a filtrate of the blood and it has a pH that influences oral and dental health. The saliva, however, is very influenced by bacteria food remnants and whatnot in the oral cavity, and saliva does not reveal as much about metabolic acid buffering.