A diagnosis is made via a medical professional’s evaluation, based on specific criteria, and laboratory and imaging tests to rule out other disorders.
No definitive test, currently, exists to diagnose schizophrenia.
A medical professional makes the diagnosis based on a comprehensive assessment of an individual’s history and symptoms.
Schizophrenia is diagnosed when both of the following are present:
- Two or more characteristic symptoms (delusions, hallucinations, disorganised speech, disorganised behaviour, negative symptoms) persist for at least six (6) months; and
- These symptoms 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 a substance use disorder or an underlying medical, neurological, or hormonal disorder, that can have features of psychosis. Examples of such disorders include brain tumours, temporal lobe epilepsy, thyroid disorders, autoimmune disorders, Huntington disease, liver disorders, side effects of drugs, and vitamin deficiencies. Testing for substance use disorder is sometimes done.
Imaging tests of the brain, such as computed tomography (CT) or magnetic resonance imaging (MRI), may be done to rule out a brain tumour. Although individuals with schizophrenia have brain abnormalities that may be seen on CT or MRI, the abnormalities are not specific enough to help in diagnosing schizophrenia.
In addition, medical professionals try to rule out a number of other mental disorders that share features with schizophrenia, such as brief psychotic disorder, schizophreniform disorder, schizoaffective disorder, and schizotypal personality disorder.