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Background: Subthreshold depression is highly prevalent in adolescence, but compared to major depressive disorder, the clinical impact is under-researched. The aim of this review was to compare subthreshold depression and major depressive disorder in adolescents by reviewing available literature on epidemiology, risk factors, illness trajectories, brain anatomy and function, genetics, and treatment response.Methods: We conducted a scoping review of papers on subthreshold depression and major depressive disorder in adolescence published in English. Studies in adults were included when research in adolescence was not available.Results: We found that individuals with subthreshold depression were similar to individuals with major depressive disorder in several regards, including female/male ratio, onset, functional impairment, comorbidity, health care utilization, suicidal ideation, genetic predisposition, brain alterations, and treatment response. Further, subthreshold depression was about two times more common than major depressive disorder.Limitations: The definition of subthreshold depression is highly variable across studies. Adolescent-specific data are limited in the areas of neurobiology and treatment.Conclusions: The findings of the current review support the idea that subthreshold depression is of clinical importance and provide evidence for a spectrum, versus categorical model, for depressive symptomatology. Given the frequency of subthreshold depression escalating to major depressive disorder, a greater recognition and awareness of the significance of subthreshold depression in research, clinical practice and policy-making may facilitate the development and application of early prevention and intervention. [ABSTRACT FROM AUTHOR]

Screening is done to improve health outcomes by identifying and effectively treating individuals with unrecognized conditions. Depression screening has been proposed to identify previously unrecognized depression cases. Including individuals already diagnosed or treated for depression in screening test accuracy studies could exaggerate accuracy and the yield of new cases from screening. The present study investigated (1) the proportion of depression screening tool accuracy primary studies published in 2018–2021 that excluded individuals with a confirmed depression diagnosis or who were already undergoing treatment; and (2) whether this has improved since the last review of studies published in 2013–2015, which found that five of 89 (5.6%) primary studies appropriately excluded such individuals. MEDLINE was searched from January 1, 2018 through May 21, 2021 for primary studies on depression screening tool accuracy. Eighteen of 106 (17.0%; 95% Confidence Interval [CI], 11.0% to 25.3%) primary studies excluded currently diagnosed or treated individuals. This was 11.4% (95% CI, 2.8% to 20.0%) greater than in similar studies published in 2013–2015. There has been an improvement since 2015, but the proportion of studies that exclude individuals already known to have depression remains low. This may bias research findings intended to inform clinical practice. [ABSTRACT FROM AUTHOR]