There is no single test that can be used to definitively diagnose schizophrenia, according to WebMD. Generally, a psychiatrist diagnoses schizophrenia after conducting sessions with the patient and interviews with the family and friends of the patient.
Generally, a diagnosis of schizophrenia is made with three guidelines in mind, reports WebMD. First, the patient must have been experiencing symptoms for at least six months. Second, the patient's life must be seriously impaired by his symptoms to the degree that maintaining normal relationships or keeping a job is difficult. Third, the symptoms must not be explainable by any other mental illness or by drug use.