How is delusional disorder diagnosed?

If symptoms are present, your doctor will perform a complete medical history and physical examination. Although there are no laboratory tests to specifically diagnose delusional disorder, the doctor might use various diagnostic tests — such as X-rays or blood tests — to rule out physical illness as the cause of your symptoms.

If the doctor finds no physical reason for the symptoms, he or she might refer the person to a psychiatrist or psychologist, health care professionals who are specially trained to diagnose and treat mental illnesses. Psychiatrists and psychologists use specially designed interview and assessment tools to evaluate a person for a psychotic disorder. The doctor or therapist bases his or her diagnosis on the person’s report of symptoms, and his or her observation of the person’s attitude and behavior.

The doctor or therapist then determines if the person’s symptoms point to a specific disorder as outlined in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), which is published by the American Psychiatric Association and is the standard reference book for recognized mental illnesses. According to the DSM-5, a diagnosis of delusional disorder is made if a person has non-bizarre delusions for at least one month and does not have the characteristic symptoms of other psychotic disorders, such as schizophrenia.

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