After a preliminary interview about your symptoms either directly or via an online psychiatric consultation, a psychiatrist determines a diagnosis. A psychiatrist may perform a few medical tests to rule out probable physical diseases, but blood tests or similar tests or scans cannot be used to determine mental health. The American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders describes the unique signs of each mental condition. This manual is used by mental health practitioners to identify mental diseases, and determine a course of treatment.