The diagnosis of schizophrenia is often not easy to make. It is not possible to make the diagnosis in one meeting. Even if the person has psychotic symptoms, that does not mean he or she has schizophrenia. It may take months or even years to see if the pattern of illness fits the description of schizophrenia.
Just as there are many causes of fever, there are many causes of psychosis. The clinician doing the evaluation will look for some of these other causes, for example, a mood disorder, a medical problem or a toxic substance. Experts know that brain function is impaired in schizophrenia, but tests that examine the brain directly cannot yet be used to make a diagnosis. A clinician may do tests such as computed tomography (CT), magnetic resonance imaging (MRI) or an electroencephalogram (EEG). These tests will help to rule out causes of the symptoms other than schizophrenia, such as a tumor or a seizure disorder.