Risk of mortality after emergency department presentation for self-harm among children and adolescents in Wales: a population-based cohort study.

Background: Self-harm in childhood and adolescence is associated with substantial morbidity and premature mortality, particularly from suicide. We aimed to quantify the risk of cause-specific and all-cause mortality following emergency department (ED) presentations for self-harm. Methods: In this retrospective population-based cohort study, we used anonymised, linked electronic health records from the Secure Anonymised Information Linkage (SAIL) Databank. We included children and adolescents aged 5-18 years who presented to EDs in Wales between 2008 and 2023. Individuals with at least one ED presentation for self-harm were assigned to the exposed group, and those with no recorded self-harm presentations formed the comparison group. Follow-up began at the index ED presentation and continued until death, possible emigration, or end of data availability. The primary outcome was suicide; secondary outcomes included accidental death, other causes of death, and all-cause mortality. Associations between self-harm and cause-specific mortality were estimated using Cox proportional hazards models adjusted for age and sex. Kaplan-Meier failure curves (1 - survival) were estimated separately for each cause of death. Findings: Between 2008 and 2023, we identified 611,336 young people who presented to EDs, of whom 14,007 (2.3%) had at least one self-harm presentation. During follow-up, 1451 deaths were recorded. Mortality was higher among those presenting with self-harm compared with controls without self-harm presentations (114 [0.8%] vs 1337 [0.2%], adjusted hazards ratio [aHR] 3.1, 95% CI 2.6-3.8). Suicide risk was markedly elevated in the first year after presentation (aHR 13.4, 95% CI 4.7-38.0) and remained increased during follow-up (aHR 4.9, 95% CI 3.4-6.9). There was a similarly increased risk of accidental death within one year (aHR 13.9, 95% CI 6.2-31.1) and after one year (aHR 5.5, 95% CI 3.9-7.7). No clear association between self-harm and other causes of death was observed. Interpretation: ED presentation for self-harm identifies young people at elevated risk of premature mortality. Preventive interventions should extend beyond suicide alone to address accidental deaths, particularly in the period immediately following presentation. Funding: McGill Global Health Programs Fellowship; John Fell Fund; NIHROxford Health Biomedical Research Centre; Academy of Medical Sciences; UK Department for Business, Energy and Industrial Strategy.