Risk factors for conversion from unipolar psychotic depression to bipolar disorder

Objectives Patients with unipolar psychotic depression ( PD ) are at high risk of developing bipolar disorder ( BD ). This conversion has important implications for the choice of treatment. This study, therefore, aimed to identify risk factors associated with diagnostic conversion from PD to BD . Methods We conducted a population‐based, historical prospective cohort study by merging data from Danish registers. Patients assigned an ICD ‐10 diagnosis of PD between 1 January 1995 and 31 December 2007 were identified in the Danish Central Psychiatric Research Register and were followed until the development of BD , death, loss to follow‐up, or 31 December 2007. Potential risk factors for conversion to BD , also defined through various Danish registers, were tested in multiple logistic regression analyses with risk expressed as adjusted odds ratios ( AOR ). Results We identified 8,588 patients with PD , of whom 609 (7.1%) developed BD during follow‐up. The following characteristics were significantly associated with diagnostic conversion from PD to BD : early onset of PD [ AOR  = 0.99 (per year of increasing age), p = 0.044], recurrent depression [ AOR  = 1.02 (per episode), p = 0.036], living alone ( AOR  = 1.29, p = 0.007), receiving a disability pension ( AOR  = 1.55, p < 0.001), and the highest educational level being a technical education ( AOR  = 1.55, p < 0.001), short‐cycle higher education ( AOR  = 2.65, p < 0.001), or medium‐cycle higher education ( AOR  = 1.75, p < 0.001). Conclusions Diagnostic conversion to BD was prevalent among patients with PD . The following characteristics were significantly associated with this conversion: early onset of PD , recurrent depression, living alone, receiving a disability pension, and the highest educational level being a technical education, short‐cycle higher education, or medium‐cycle higher education.