Diagnosis of borderline personality disorder is based on a clinical assessment by a mental health professional. The best method is to present the criteria of the disorder to a person and to ask them if they feel that these characteristics accurately describe them. Actively involving people with BPD in determining their diagnosis can help them become more willing to accept it. Although some clinicians prefer not to tell people with BPD what their diagnosis is, either from concern about the stigma attached to this condition or because BPD used to be considered untreatable, it is usually helpful for the person with BPD to know their diagnosis. This helps them know that others have had similar experiences and can point them toward effective treatments.
In general, the psychological evaluation includes asking the patient about the beginning and severity of symptoms, as well as other questions about how symptoms impact the patient's quality of life. Issues of particular note are suicidal ideations, experiences with self-harm, and thoughts about harming others. Diagnosis is based both on the person's report of their symptoms and on the clinician's own observations. Additional tests for BPD can include a physical exam and laboratory tests to rule out other possible triggers for symptoms, such as thyroid conditions or substance abuse. The ICD-10 manual refers to the disorder as emotionally unstable personality disorder and has similar diagnostic criteria. In the DSM-5, the name of the disorder remains the same as in the previous ions.
The Diagnostic and Statistical Manual of Mental Disorders fifth ion (DSM-5) has removed the multiaxial system. Consequently, all disorders, including personality disorders, are listed in Section II of the manual. A person must meet 5 of 9 criteria to receive a diagnosis of borderline personality disorder. The DSM-5 defines the main features of BPD as a pervasive pattern of instability in interpersonal relationships, self image, and affect, as well as markedly impulsive behavior. In addition, the DSM-5 proposes alternative diagnostic criteria for Borderline personality disorder in section III, "Alternative DSM-5 Model for Personality Disorders." These alternative criteria are based on trait research and include specifying at least four of seven maladaptive traits. According to Marsha Linehan, many mental health professionals find it challenging to diagnose BPD using the DSM criteria, since these criteria describe such a wide variety of behaviors. To address this issue, Linehan has grouped the symptoms of BPD under five main areas of dysregulation: emotions, behavior, interpersonal relationships, sense of self, and cognition.
The World Health Organization's ICD-10 defines a disorder that is conceptually similar to borderline personality disorder, called emotionally unstable personality disorder. Its two subtypes are described below.