Unfortunately, borderline personality disorder is often underdiagnosed or misdiagnosed.
A mental health professional experienced in diagnosing and treating mental disorders—such as a psychiatrist, psychologist, clinical social worker, or psychiatric nurse—can detect borderline personality disorder based on a thorough interview and a discussion about symptoms. A careful and thorough medical exam can help rule out other possible causes of symptoms. No single test can diagnose borderline personality disorder.
The mental health professional may ask about symptoms and personal and family medical histories, including any history of mental illnesses. This information can help the mental health professional decide on the best treatment. In some cases, co-occurring mental illnesses may have symptoms that overlap with borderline personality disorder, making it difficult to distinguish borderline personality disorder from other mental illnesses. For example, a person may describe feelings of depression but may not bring other symptoms to the mental health professional's attention.