Mortality in children and adolescents who present to hospital following non-fatal self-harm: an observational cohort study based on the Multicentre Study of Self-harm in England

Background
Self-harm and suicide in children and adolescents are both growing problems, with self-harm associated with a significant risk of subsequent death, particularly suicide. Long-term follow-up studies are necessary to examine the extent and nature of this association.
Method
We used data from the Multicentre Study of Self-harm in England to investigate deaths following self-harm to the end of 2015 in 9173 10-18 year-olds who had 13,175 self-harm presentations to the emergency departments of the study hospitals between 2000 and 2013. Deaths were identified through the Office for National Statistics via linkage with data from NHS Digital. Risk factors were examined using survival models.
Findings
By the end of the follow-up period 124 (1%) of the cohort (N=9173) had died. Fifty-five (44%) of the deaths were suicides, 27 (22%) accidental and 42 (34%) due to other causes. Most suicide deaths involved self-injury (n=45, 82%). There was often a method switch from self-harm to suicide, especially from self-poisoning to hanging or asphyxiation. The incidence of suicide in the 12 months after self-harm was over 30 times the rate expected in the general population of 10-18 year-olds in England (SMR 31·0, 95% CI 18·2-30·9). The majority of the suicides (n=42, 77%) occurred after age 18 years and the incidence rate remained similar over more than 10 years follow-up. Increased suicide risk was associated with male gender, being an older teenager, use of self-injury (especially hanging/asphyxiation) for self-harm and repeating self-harm. Accidental poisoning deaths involving substance misuse were especially frequent in males.
Interpretation
Children and adolescents who self-harm have a considerable risk of future suicide, especially males, older teenagers, and those who repeat self-harm. Risk may persist over several years. Switching of method from self-poisoning in self-harm to self-injury, especially hanging or asphyxiation, for suicide is common. Self-harm is also associated with risk of death from accidental poisoning, particularly involving drugs of abuse, especially in males.