The Exploratory Treatment
There are certain diseases which have identical causes, preliminary signs, and symptoms. For example, fever may be a symptom of typhoid, malaria or pneumonia. In ancient times, when modern scientific testing techniques did not exist, a specific diagnosis was aided by upashaya. This involves investigating and eliminating particular diseases through diet, herbal remedies or physical therapies that can help to make an exact diagnosis.

For example, in the case of fever, the doctor might try prescribing anti-malarial herbs to see if the symptoms are alleviated. If that reduces the severity of symptoms, it confirms that the patient has malaria. If anti-malarial herbs makes no difference, malaria can be eliminated as one of the potential diseases. Similarly, dietary changes may be recommended by a doctor to confirm an opinion about a suspected diagnosis.

Source: http://www.jiva.com/ayurveda/about-ayurveda/110.html