Objective: Bipolar disorder and borderline personality disorder share some clinical features and have similar correlates. It is, therefore, not surprising that differential diagnosis is sometimes difficult. The Mood Disorder Questionnaire (MDQ) is the most widely used screening scale for bipolar disorder. Prior studies found a high false-positive rate on the MDQ in a heterogeneous sample of psychiatric patients and primary care patients with a history of trauma. In the present report from the Rhode Island Methods to Improve Diagnostic Assessment and Services project, we examined whether psychiatric outpatients without bipolar disorder who screened positive on the MDQ would be significantly more often diagnosed with borderline personality disorder than patients who did not screen positive.

Method: The study was conducted from September 2005 to November 2008. Five hundred thirty-four psychiatric outpatients were interviewed with the Structured Clinical Interview for DSM-IV and Structured Interview for DSM-IV Personality Disorders and asked to complete the MDQ. Missing data on the MDQ reduced the sample size to 480. Approximately 10% of the study sample were diagnosed with a lifetime history of bipolar disorder (n = 52) and excluded from the initial analyses.

Results: Borderline personality disorder was 4 times more frequently diagnosed in the MDQ positive group than the MDQ negative group (21.5% vs 4.1%, P < .001). The results were essentially the same when the analysis was restricted to patients with a current diagnosis of major depressive disorder (27.6% vs 6.9%, P = .001). Of the 98 patients who screened positive on the MDQ in the entire sample of patients, including those diagnosed with bipolar disorder, 23.5% (n = 23) were diagnosed with bipolar disorder, and 27.6% (n = 27) were diagnosed with borderline personality disorder.

Conclusions: Positive results on the MDQ were as likely to indicate that a patient has borderline personality disorder as bipolar disorder. The clinical utility of the MDQ in routine clinical practice is uncertain.