Background: Patients with bipolar disorder (BD) and depressive episodes are usually diagnosed with major depressive disorder (MDD). It is clinically important to estimate diagnostic conversion rate from MDD to BD and identify factors characterizing MDD patients at highest risk. We investigated conversion rate from depression to BD, stratified by age and sex, and associated psychopharmacological treatment patterns. Methods: Data were extracted from the National Health Insurance to include 817,759 patients 18 years or older with new-onset antidepressant-treated depression between 2011 and 2015. We estimated rate of conversion from unipolar depression to BD stratified by age and sex during follow-up (357,343 person-years) and investigated the related medication patterns. Results: During follow-up (median, 155 days; range, 2–1,442 days), 19,179 patients had diagnostic conversion to BD. Conversion rate was highest for patients aged 18–29 years; it gradually decreased with age until 60–69 years. Overall conversion rate to BD was 58.48 per 1,000 person-years for males and 50.97 per 1,000 person-years for females. For patients aged 18–39 years, the rate was higher for females. Patients with conversion to BD were prescribed more antidepressants. When the diagnosis changed to BD, 51% of patients were prescribed additional antipsychotics and/or mood stabilizers. Limitations: The limited follow-up period may have underestimated conversion rate to BD. Data were restricted to participants with pharmaceutically treated depression. Conclusions: The rate of diagnostic conversion from depression to BD differed by sex and age and was highest for females aged 18–29 years. Diagnostic conversion was accompanied by relevant prescription changes.
- Bipolar disorder
- Diagnostic conversion
- Psychopharmacological treatment
- Register-based study