One-year prevalence and psychiatric comorbidity of borderline personality disorder in a medical certificate population: a registry study of psychiatric outpatients in community mental health care in the city of Oulu

Objective: Borderline personality disorder (BPD) is a common disorder in healthcare settings but estimates of BPD prevalence vary greatly. This study aimed to estimate the one-year prevalence of BPD in psychiatric outpatients and analyze the psychiatric comorbidity presented with BPD.Method: The data comprised 18-60-year-old patients who had a BPD diagnosis recorded in their medical certificate B (mcB) and were treated in specialized psychiatric outpatient services in the city of Oulu, northern Finland, in 2014. An mcB is a comprehensive summary of a patient's medical history written by a doctor, and patients need it in the Finnish healthcare system when applying for social benefits and rehabilitation measures.Results: The prevalence of BPD was 12.8% among patients with an mcB treated in the psychiatric outpatient services. BPD was 3.0 times more common in female than male psychiatric outpatients with an mcB. The most common comorbid psychiatric disorders written in mcBs of BPD patients were mood (81.0%) and anxiety (39.2%) disorders. The only statistically significant gender difference was found in behavioral and emotional disorders (16.7% in men, 1.6% in women).Conclusions: The mcB-based BPD prevalence estimate and psychiatric comorbidity was consistent with previous studies researching psychiatric outpatients with BPD. McBs appear to be a reliable and comprehensive data source for diagnostic information in research.