BACKGROUND Self-harm is a recognised predictor of suicide and is most common in those aged under 25 years. The aims of this study were to describe the characteristics of young people who present with self-harm; quantify the risk of suicide and other causes of death during follow up, and to identify factors associated with mortality risk.

METHODS The Northern Ireland Registry of Self-Harm (NIRSH) is a national registry capturing complete data on all presentations made to the 12 Emergency Departments (EDs) in Northern Ireland (NI). Data relating to self-harm presentations registered in the NIRSH between 2012 and 2015 were linked to primary care registrations and death records up until 31st December 2018. Logistic regression was employed to examine the factors associated with self-harm. Cox regression was used to estimate mortality risk following self-harm and explore the associated risk factors.

RESULTS The cohort consisted of 390,740 individuals aged 10-24 years registered with a General Practitioner (GP) in NI. During follow-up, 4,450 individuals presented with self-harm. Rates of self-harm were highest in females, those aged 20-24 years (OR  = 3.53, 95% CI 3.28-3.80, p < .001), and in the most deprived areas (OR  = 2.71, 95% CI 2.45-2.99, p < .001). Thirty five individuals who presented with self-harm died by suicide, accounting for 23% of all suicide deaths in the cohort. Suicide risk was increased 19-fold in those who presented with self-harm after adjustment for age, sex and area-level factors (HR  = 19.00, 95% CI 12.80-28.21, p < .001). Increased suicide risk was observed in males (HR  = 2.04, 95% CI 0.99-4.23, p = .05) and those using more violent methods of self-injury (HR  = 3.89, 95% CI 1.65-9.13, p < .001).

CONCLUSIONS Young people who self-harm are at a significantly greater risk of suicide. Almost a quarter of young people who died by suicide in NI had presented to EDs with self-harm, highlighting that the ED may provide a nodal point of intervention among a typically hard to identify and reach population.