how is schizophrenia diagnosed

Diagnosis of schizophrenia involves ruling out other mental health disorders and determining that symptoms are not due to substance abuse, medication or a medical condition. Determining a diagnosis of schizophrenia may include:

Physical exam. This may be done to help rule out other problems that could be causing symptoms and to check for any related complications.
Tests and screenings. These may include tests that help rule out conditions with similar symptoms, and screening for alcohol and drugs. The doctor may also request imaging studies, such as an MRI or CT scan.

Psychiatric evaluation. A doctor or mental health professional checks mental status by observing appearance and demeanor and asking about thoughts, moods, delusions, hallucinations, substance use, and potential for violence or suicide. This also includes a discussion of family and personal history.
Diagnostic criteria for schizophrenia. A doctor or mental health professional may use the criteria in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), published by the American Psychiatric Association.