Clinical and subthreshold depression in an epidemiologic sample of adolescents.

Objective: Understanding the clinical continuum of depression (encompassing Major Depressive Disorder (MDD) and Subthreshold Depression (SD)) is fundamental to developing detection and prevention, especially among adolescents where onset is common. Using an epidemiologic adolescent sample, this study examined the prevalence of MDD and SD, and compared psychosocial outcomes with healthy controls (HCs).

Method: A total of 2295 adolescents aged 12-17 were randomly selected from schools across Hong Kong. Structured diagnostic interviews assessed 12-month prevalences of MDD and SD. These groups were compared against HCs on demographics, impairment, and subjective well-being. Associations of impairment or well-being with depressive symptoms were examined in the MDD and SD groups.

Results: The sample consisted of 98 adolescents with MDD, 179 with SD, and 2018 HCs, yielding prevalence estimates of 4.3 % and 7.8 % for MDD and SD respectively. Both were more common in girls. While the risk of having other psychiatric disorders was 3.43 times higher in MDD than SD, as much as 61.5 % of the latter met the diagnostic criteria for at least one disorder. Albeit at a lower level than MDD, SD showed dampened well-being relative to HCs, with 20.6 % exhibiting severe impairment. Among MDD and SD participants, depressed/irritable mood and concentration difficulty predicted worse impairment, whereas recurrent thoughts of death predicted poorer well-being.

Conclusion: SD is more prevalent than MDD among adolescents. Despite not being a diagnostic condition, SD is associated with comparable psychiatric comorbidity and functional impact. More research on how subthreshold depressive symptoms convert into full-blown disorders is warranted.