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Q In patients who present to the emergency department (ED) with self harm, can a simple clinical rule predict repetitions of self harm or suicide in the next 6 months?
Clinical impact ratings Paediatrics (general) ★★★★★★☆ Psychiatry ★★★★★★☆ Emergency medicine ★★★★★☆☆
prospective cohort study with separate derivation and validation data sets.
5 EDs in Manchester and Salford, UK.
9086 episodes of self harm (intentional self poisoning or self injury) in patients 11–98 years of age (median age 30 y, 56% women). Patients who did not wait for assessment or refused treatment were excluded.
Description of prediction guide:
the patient was considered to be at moderate or high risk of repeat self harm or suicide if any 1 of the 4 components of the Manchester Self Harm Rule was present: (1) history of self harm, (2) previous psychiatric treatment, (3) current psychiatric treatment, or (4) benzodiazepine use in this attempt.
suicide or repeat visit to the ED for self harm within 6 months of the index ED visit.
In each data set, 78% of patients were classified as moderate or high risk. 17% of patients in the derivation set and 18% in the validation set had repeat ED visits for self harm or died by suicide within 6 months. The table shows the diagnostic accuracy of the Manchester Self Harm Rule in the derivation and validation sets. The rule identified all 22 patients who committed suicide within 6 months.
The Manchester Self Harm Rule had good sensitivity but poor specificity for predicting repetitions of self harm or suicide in patients who presented to the emergency department with self harm.
A modified version of the abstract appears in Evidence-Based Nursing.
The clinical prediction guide of Cooper et al correctly identified about 95% of people who were going to repeat self harm in the next 6 months. This result is not surprising because the guide identified most people who presented (about 4 out of 5 people) as being at high or moderate risk. Probably more usefully, when the decision rule identified someone as low risk (about 1 in 5 who presented), it was correct about 95% of the time.
The study by Cooper et al is a good example of how to derive a clinical decision rule. However, several caveats should be mentioned. Firstly, 1 in 5 people who presented in these EDs received no assessment of any sort. This clinical decision rule applies only to those who were seen. Secondly, it is difficult to make any clinical sense of the fact that taking a benzodiazepine overdose puts someone in a moderate or high risk category. Lastly, using the authors’ own data from a previous study,1 the clinical decision rule is little better than a “clinical global assessment.” In that previous study, using some of the same data as in the current study, the positive predictive value of a global assessment by ED staff was 16% and the negative predictive value was 93%.1 For assessments by mental health clinicians, the respective figures were 18% and 90%. The clinical decision rule described here does not mark much of an advance on these figures.
Deriving clinical rules to identify patients who are at high risk of repetition or suicide has several problems. Firstly, such rules usually result in many false positives, as in this study, potentially leading to a waste of resources. Secondly, they are based on the assumption that the task of risk assessment is to predict the future. This is not the case: it is about identifying and managing risk. Lastly, less than half the premature mortality following self harm is by suicide. The rest is from other diseases and accidents. Clinical decision rules such as the one in this study do not address this problem and are of limited clinical use.
For correspondence: Dr J Cooper, Centre for Suicide Prevention, University of Manchester, Manchester, UK.
Sources of funding: Manchester Health Authority; South Manchester University Hospitals NHS Trust; Central Manchester and Manchester Children’s University Hospitals NHS Trust; Pennine Acute NHS Trust; Mental Health Services of Salford NHS Trust.
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