Borderline personality disorder (BPD) is diagnosed through a clinical evaluation by a mental health professional, typically a psychiatrist or psychologist, who assesses whether you meet at least 5 of 9 specific behavioral and emotional criteria. There is no blood test or brain scan for BPD. Diagnosis relies on a detailed review of your emotional patterns, relationships, and behavior over time.
The 9 Diagnostic Criteria
The DSM-5, which is the standard diagnostic manual used in the United States, defines BPD as a pervasive pattern of instability in relationships, self-image, and emotions, combined with marked impulsivity. These patterns must begin by early adulthood and show up across different areas of your life. To receive a diagnosis, you need to meet at least 5 of these 9 criteria:
- Fear of abandonment: Frantic efforts to avoid real or imagined abandonment.
- Unstable relationships: A pattern of intense relationships that swing between idealizing someone and devaluing them.
- Unstable sense of self: A markedly shifting self-image or sense of who you are.
- Dangerous impulsivity: Impulsive behavior in at least two areas that could cause harm, such as reckless spending, substance use, binge eating, or unsafe driving.
- Self-harm or suicidal behavior: Recurrent suicidal gestures, threats, or self-injuring behavior.
- Rapid mood shifts: Intense emotional reactions, often lasting a few hours and rarely more than a few days, triggered by events around you.
- Chronic emptiness: A persistent feeling of being empty inside.
- Intense anger: Inappropriate or hard-to-control anger, frequent temper outbursts, or constant irritability.
- Stress-related paranoia or dissociation: Brief episodes of paranoid thinking or feeling disconnected from reality during high stress.
Not everyone with BPD experiences all nine. Two people with the diagnosis can look quite different from each other depending on which five or more criteria they meet.
What the Evaluation Looks Like
A primary care doctor can raise the possibility of BPD, but a formal diagnosis typically comes from a psychiatrist or clinical psychologist. Your doctor may refer you to one of these specialists for a more thorough assessment.
The evaluation usually involves a structured clinical interview. One widely used tool is the Structured Clinical Interview for DSM-5 Personality Disorders (SCID-5-PD), which walks through each criterion systematically. The clinician asks detailed questions about your relationships, emotional reactions, self-image, and impulsive behaviors, looking for patterns that are longstanding rather than tied to a single episode or life event. They’ll also ask about your history, including childhood experiences, past treatment, and substance use.
Some clinicians also use screening questionnaires as a starting point. The McLean Screening Instrument for BPD is a 10-item true-or-false questionnaire where a score of 7 or higher is considered highly suggestive of BPD. These tools don’t replace a full clinical evaluation, but they can help flag who needs a deeper assessment.
Diagnosis in Teenagers
BPD can be reliably diagnosed in adolescents as young as 11 years old, using the same criteria applied to adults. The key difference is that symptoms must have been present for at least one year, and they must be clearly distinct from normal developmental changes. The traits also need to cause noticeable problems at school, in relationships, or significant personal distress. Many clinicians have historically been reluctant to diagnose BPD in teens, but current evidence supports early identification because it opens the door to treatment sooner.
Why BPD Is Often Confused With Bipolar Disorder
BPD and bipolar disorder share symptoms like mood instability, impulsivity, and anger, which leads to frequent confusion between the two. Roughly 20% of people with BPD also have bipolar disorder, and about 15% of people with bipolar disorder also have BPD, making the overlap even harder to untangle.
The most useful distinction is in how mood shifts work. In BPD, mood changes are typically reactive, meaning they’re triggered by interpersonal events like feeling rejected or abandoned. These shifts are intense but brief, usually lasting hours rather than days. In bipolar II disorder, mood episodes tend to be more autonomous, arising without a clear external trigger, and hypomanic episodes last days or longer. A person with BPD rarely experiences sustained euphoria, while someone with bipolar II may have distinct periods of elevated mood and energy. These differences in timing and trigger help clinicians tell the two apart, though some people genuinely have both conditions.
How BPD Differs From Complex PTSD
Complex PTSD (CPTSD) is another condition with significant symptom overlap. Both involve problems with emotional regulation, self-concept, and relationships. The difference lies in how those problems show up. In CPTSD, the sense of self is persistently negative: people tend to feel fundamentally broken or worthless. In BPD, the sense of self is unstable, shifting between positive and negative, sometimes rapidly. Relationship difficulties also differ. People with CPTSD tend toward avoidance and disconnection, pulling away from others. People with BPD more often show a pattern of volatile, intense involvement with others, driven by efforts to avoid being abandoned.
Common Comorbidities That Complicate Diagnosis
BPD rarely shows up alone. Depression, anxiety disorders, PTSD, eating disorders, and substance use disorders frequently co-occur, and their symptoms can mask or mimic BPD features. Someone might be treated for depression for years before a clinician recognizes that the underlying pattern is BPD. The reverse also happens: BPD symptoms like emotional reactivity and impulsivity get attributed to bipolar disorder, leading to medication-focused treatment that doesn’t address the core problem.
This is one reason the diagnostic process takes time. A skilled clinician needs to look past the surface-level symptoms and identify the deeper pattern of instability across relationships, identity, and emotions. A single appointment is rarely enough.
BPD Diagnosis Can Change Over Time
One of the most encouraging findings about BPD is that the diagnosis is not necessarily permanent. A landmark 10-year study found that 85% of people with BPD achieved remission, defined as meeting two or fewer of the nine criteria for at least 12 months. This doesn’t mean the person never struggles again, but it does mean the full pattern of symptoms can resolve substantially with time and treatment. The diagnosis reflects where you are, not a fixed identity.