If symptoms of schizophrenia are present, the doctor will perform a complete medical history and sometimes a physical exam. While there are no laboratory tests to specifically diagnose schizophrenia, the doctor may use various tests, and possibly blood tests or brain imaging studies, to rule out another physical illness or intoxication (substance-induced psychosis) as the cause of the symptoms.
If the doctor finds no other physical reason for the schizophrenia symptoms, he or she may refer the person to a psychiatrist or psychologist, mental health professionals who are specially trained to diagnose and treat mental illnesses. Psychiatrists and psychologists use specially designed interviews and assessment tools to evaluate a person for a psychotic disorder. The therapist bases his or her diagnosis on the person's and family's report of symptoms and on his or her observation of the person's attitude and behavior. A person is considered to have schizophrenia if he or she has characteristic symptoms that last for at least six months.