There is, as yet, no simple lab test to make a diagnosis. Therefore, the diagnosis is based on the symptoms - what the person says and what the doctor observes. To reach a diagnosis of schizophrenia, other possible causes such as drug abuse, epilepsy, brain tumour, thyroid or other metabolic disturbances, as well as other physical illnesses that have symptoms like schizophrenia, such as hypoglycemia and Wilson's disease, must be ruled out.
Some patients show the symptoms of both schizophrenia and manic depression.
Its relation to schizophrenia is unclear at present. A diagnostic system for mental illness widely used in North America was developed by a task force of the American Psychiatric Association. Since DSM-III was published in 1980, further refinements have taken place. No matter what happens during the first visit to the doctor, the diagnosis of schizophrenia usually takes a long time. There are also many differences among individuals in the way in which symptoms present themselves.