A widespread screening tool for bipolar disorder—the Mood Disorder Questionnaire (MDQ)—often incorrectly labeled people as bipolar when they actually had borderline personality disorder (BPD), according to a study published online March 23 in The Journal of Clinical Psychiatry.

Bipolar disorder and BPD share some similar characteristics, including mood swings and impulsive behavior. But they are significantly different psychological disorders, and their treatments differ substantially. An accurate diagnosis of either bipolar or BPD is vital so people suffering from one or the other can receive the appropriate treatment.

One tool, the MDQ, is widely used to diagnose bipolar disorder. It is a short questionnaire that most clinicians can easily use. It can also be self-administered by people who suspect they have bipolar disorder.

To determine the effectiveness of the MDQ, Mark Zimmerman, MD, and his colleagues from the Rhode Island Hospital compared the results from the MDQ with more structured expert interviews by mental health professionals in people seeking outpatient care between September 2005 and November 2008 at the Rhode Island Hospital psychiatric clinic.

Zimmerman’s team found that nearly 28 percent of people who the MDQ indicated had bipolar disorder actually had BPD. In fact, people who scored as bipolar on the MDQ were four times as likely to later be diagnosed with BPD than people whom the MDQ did not score as bipolar.

“Without an accurate diagnosis of borderline personality disorder, we may have many people in treatment who are taking medications that will not work to alleviate the characteristics of the condition from which they really suffer,” said Zimmerman in a Rhode Island Hospital press release on the study. “In addition, patients with unrecognized borderline personality disorder will not be treated with one of the effective psychotherapies for this condition. It is therefore vital that we develop or identify a more accurate method to distinguish between these two conditions, and adopt it into clinical practice.”