I spent the summer before my senior year of veterinary school working in a clinic in Orange County, California. One of the veterinarians confided something to me that I have reflected on countless times in the last 13 years. As a wide-eyed veterinary student, I couldn't fathom where that philosophy originated. As defined by Dorland's Medical Dictionary, diagnosis is the art of distinguishing one disease from another, the determination of the nature of a case of disease. Certainly a battery of tests are not needed to diagnose all diseases.
Most cases require the use of all three diagnostic tools.
Think of them as the legs of a tripod, supporting a diagnosis. If one of the legs is missing or faulty, then the diagnosis is less valid. Veterinarians are unique among medical professionals. We cannot solely concentrate on our patient's medical conditions and needs. Each patient has a human owner who must also be factored into the equation.