title: Conversion from depression to bipolar disorder in a cohort of young people in England, 1999-2011: A national record linkage study.
abstract: OBJECTIVE
  To estimate the conversion rate from unipolar depression (ICD10 codes F32-F33) to bipolar disorder (BP) (ICD10 codes F31) in an English national cohort. It was hypothesised that early-onset BP (age <18 years) is a more severe form of the disorder, with a more rapid, and higher rate of conversion from depression to BP.
  
  
  METHODS
  This record linkage study used English national Hospital Episode Statistics (HES) covering all NHS inpatient and day case admissions between 1999 and 2011.
  
  
  RESULTS
  The overall rate of conversion from depression to BP for all ages was 5.65% (95% CI: 5.48-5.83) over a minimum 4-year follow-up period. The conversion rate from depression to BP increased in a linear manner with age from 10-14 years - 2.21% (95% C: 1.16-4.22) to 30-34 years - 7.06% (95% CI: 6.44-7.55) (F1,23=77.6, p=0.001, R(2)=0.77). The time to conversion was constant across the age range. The rate of conversion was higher in females (6.77%; 95% CI: 6.53-7.02) compared to males, (4.17%; 95% CI: 3.95-4.40) (χ(2)=194, p<0.0001), and in those with psychotic depression 8.12% (95% CI: 7.65-8.62) compared to non-psychotic depression 5.65% (95% CI: 5.48-5.83) (χ(2)=97.0, p<0.0001).
  
  
  CONCLUSIONS
  The study was limited to hospital discharges and diagnoses were not standardised.
  
  
  CONCLUSIONS
  Increasing conversion rate from depression to bipolar disorder with age, and constant time for conversion across the age range does not support the notion that early-onset BP is a more severe form of the disorder.
authors.affiliation: Highfield Unit, Warneford Hospital, Oxford OX3 7JX United Kingdom. Electronic address: anthony.james@psych.ox.ac.uk.
authors.forename: Anthony
authors.initials: A
authors.lastname: James
authors.affiliation: Unit of Health-Care Epidemiology, Nuffield Department of Population Health, University of Oxford, Old Road Campus, Oxford OX3 7LF United Kingdom.
authors.forename: Clare J
authors.initials: CJ
authors.lastname: Wotton
authors.affiliation: Department of Psychiatry, Mathison Centre for Mental Health Research and Education, Hospital Drive NW, Calgary, AB, Canada T2N.
authors.forename: Anne
authors.initials: A
authors.lastname: Duffy
authors.affiliation: Unit of Health-Care Epidemiology, Nuffield Department of Population Health, University of Oxford, Old Road Campus, Oxford OX3 7LF United Kingdom.
authors.forename: Uy
authors.initials: U
authors.lastname: Hoang
authors.affiliation: Unit of Health-Care Epidemiology, Nuffield Department of Population Health, University of Oxford, Old Road Campus, Oxford OX3 7LF United Kingdom.
authors.forename: Michael
authors.initials: M
authors.lastname: Goldacre
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D001714:Bipolar Disorder / Q000175:diagnosis / Q000453:epidemiology*; D002648:Child; D015331:Cohort Studies; D003866:Depressive Disorder / Q000453:epidemiology*; D004739:England / Q000453:epidemiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D017678:Sex Distribution; D055815:Young Adult
keywords: Bipolar disorder; Conversion; Depression