Diagnosis

No definitive test exists to diagnose schizophrenia. A doctor makes the diagnosis based on a comprehensive assessment of a person's history and symptoms. Schizophrenia is diagnosed when symptoms persist for at least 6 months and cause significant deterioration in work, school, or social functioning. Information from family members, friends, or teachers is often important in establishing when the disorder began.

Laboratory tests are often done to rule out substance abuse or an underlying medical, neurologic, or hormonal disorder that can have features of psychosis. Examples of such disorders include brain tumors, temporal lobe epilepsy, thyroid disorders, autoimmune disorders, Huntington's disease, liver disorders, and side effects of drugs. Testing for drug abuse is sometimes done.

People with schizophrenia have brain abnormalities that may be seen on a computed tomography (CT) or magnetic resonance imaging (MRI) scan. However, the abnormalities are not specific enough to help in diagnosing schizophrenia.