Faculty of Medicine and Health Services, University of Newcastle, Suicide Prevention Research Unit, Centre for Mental Health Studies, Newcastle, and Department of ConsultationLiaison Psychiatry, Newcastle Mater Misericordiae Hospital, Newcastle, New South Wales, Australia
Discipline of Paediatrics, Dunedin School of Medicine, University of Otago, New Zealand
Discipline of Clinical Pharmacology, Faculty of Medicine and Health Sciences, University of Newcastle and Department of Clinical Toxicology and Pharmacology, Newcastle Mater Misericordiae Hospital, Newcastle
Australian Institute of Health and Welfare, Canberra, Australia
Correspondence: David M. Reith, Discipline of Paediatrics, Dunedin School of Medicine, University of Otago, New Zealand. E-mail: david.reith{at}stonebow.otago.ac.nz
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ABSTRACT |
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Aims To identify changes in clinical presentation predictive of suicide in patients treated for repeated episodes of self-poisoning.
Method A nested casecontrol study used the Hunter Area Toxicology Service database to identify exposure variables and the National Death Index to identify suicide. Cases were patients who had hospital treatment on more than one occasion between 15 January 1987 and 31 December 2000.
Results There were 31 cases, for which 93 controls were selected. Study variables associated with an increased risk of subsequent suicide were an increase in the number of drugs ingested (odds ratio 2.59, 95% CI 1.484.51), an increase in the dose ingested (OR 1.33, 95% CI 1.011.76), an increase in coma score (OR 1.71, 95% CI 1.112.66), a decrease in Glasgow Coma Score (OR 1.21, 95% CI 1.031.43) and an increase in drug or alcohol misuse (OR 2.33, 95% CI 1.065.10).
Conclusions Patients who have escalating severity of self-poisoning episodes are at high risk of completed suicide.
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INTRODUCTION |
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METHOD |
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A validated, pre-formatted admission sheet was used by medical staff (usually in the emergency department) to record the history and physical examination at the time of admission (Buckley et al, 1999). Psychiatric diagnosis was made according to DSMIIIR or DSMIV (American Psychiatry Association, 1987, 1994) and confirmed at a weekly meeting. Individual DSM diagnoses were then mapped to DSMIV major diagnostic categories (mood disorder, substance-related disorder, personality disorder, schizophrenia and other psychotic disorder) for all analyses. These data and additional information from the medical record were entered into the database by two trained personnel, masked to any study hypotheses, at the time of patient discharge. Suicide was identified through data linkage with the National Death Index of the Australian Institute of Health and Welfare (Reith et al, 2004) and was determined from death certificate data. The 14-year period selected for the study was 15 January 1987 to 31 December 2000, with data linkage up to 31 December 2000.
A control group was selected from the group of patients in the Hunter Area Toxicology Service database who had been treated for self-poisoning on two or more occasions over the same period, but who had not subsequently died by suicide. Patients treated for occupational poisoning or envenomation were excluded, but all deliberate self-poisoning, recreational (drug misuse) and accidental poisoning admissions were included. The Toxicology Service uses the definition of deliberate self-poisoning originally defined by Bancroft et al:
The deliberate ingestion of more than the prescribed amount of medicinal substances, or ingestion of substances never intended for human consumption, irrespective of whether harm was intended (Bancroft et al, 1975).
Three controls were selected for each case. The controls were matched for gender and 10 year age group, and were selected from within the age group and gender strata randomly using the random number generator function within Excel. Odds ratios and 95% confidence intervals (CIs) were calculated using conditional logistic regression for matched casecontrol groups using Stata (Stata, 2003). The grouping variable was the age and gender strata for the cases and the matched controls.
The independent variables studied were similar to those used as indicators of medical severity in previous studies of outcome and comparative toxicity in self-poisoning (Reith et al, 2004):
The variables that were associated with subsequent suicide were then tested for their clinical usefulness as predictors of suicide (Sacket, 1992). Continuous variables were assessed using receiver operating characteristic (ROC) plots, and the cut-off points that resulted in the greatest proportion of correct classifications (i.e. patients correctly classified as suicide or not suicide by the test) were used to generate dichotomous variables. These variables were then assessed for their suitability as predictors by calculating sensitivity, specificity and the respective 95% confidence intervals using Stata. Positive predictive values and negative predictive values were not calculated because these variables would have been biased by the pre-test probabilities of the sample being affected by the casecontrol design.
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RESULTS |
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The indicators of medical seriousness associated with subsequent suicide were an increase in coma score and a decrease in GSC score (both indicating greater degrees of coma) in the cases compared with the controls (Table 2). As indicators of intent, the number of medications, number of tablets and total dose ingested increased from first to last visit in the cases, but remained stable or decreased in the controls. This indicated a significantly increased poison exposure from first to last presentation in the case group relative to the control group. There was also a worsening in drug and alcohol status in the case group compared with the control group. There was no significant change in time to presentation, nor in intensive care unit admission or length of stay. There was no significant change in the patterns of poison exposure. There was no significant difference in change in length of stay, psychiatric diagnosis or discharge destination between the groups.
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When the significant variables were examined for their sensitivity and specificity as tests for patients who would subsequently kill themselves, none was sufficiently useful to be used alone as a screening test for subsequent completed suicide (Table 3). The most promising predictor variable was the change in the number of tablets ingested, with an area under the ROC curve of 0.73 (95% CI 0.590.88) (Fig. 1). An increase of 70 or more in the number of tablets ingested had a high specificity, and the best sensitivity of any individual test (Table 3). Combining this with deterioration in drug and alcohol misuse status increased the sensitivity to 47%. However, combining an increase of 70 or more in the number of tablets ingested with a decrease in GCS score of 2 or more resulted in the best combined test, with a sensitivity of 53% and a specificity of 87%. When tested for their association with subsequent suicide, as a post hoc analysis, the odds ratio for a 70 or more increase in tablets ingested was 3.59 (95% CI 0.983.15), for a two or more increase in number of drugs ingested was 3.60 (95% CI 1.0312.53) and for a decrease in GCS score of 2 or more was 5.36 (95% CI 1.3421.53).
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DISCUSSION |
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Risk factors for suicide after self-harm
People who deliberately harm themselves have an increased risk of suicide
(Owens et al, 2002).
Previously identified risk factors for subsequent suicide following deliberate
self-harm include previous self-harm, male gender, older age, psychiatric
illness (particularly schizophrenia, depression, bipolar disorder and
substance-related disorders), medical illness and substance misuse
(Suokas et al, 2001;
Beautrais, 2003). Specifically
following deliberate self-poisoning, identified additional risk factors for
completed suicide include psychiatric disorders of childhood, male gender,
increasing age, more than one previous suicide attempt, living alone, migrant
status and being widowed or separated
(Reith et al,
2004).
Our study showed that an increase in some markers of the severity of self-poisoning episodes was associated with subsequent death by suicide. The indicators of increased severity were indicators of potential physical harm (such as coma score) and increased severity of poison exposure. An increase in ingested dose of 70 or more tablets or capsules, an increase of two or more in the number of different agents ingested and an increase of 50 or more in the number of defined daily doses ingested were highly specific for subsequent suicide. These indicators had much greater specificity than previously identified indicators of future suicide such as Becks Hopelessness Scale: 51% for hospitalised patients with suicidal ideation and 41% for psychiatric out-patients (Beck et al, 1985, 1990). However, the sensitivity of Becks Hopelessness Scale was greater: 91% for hospitalised patients with suicidal ideation and 94% for psychiatric out-patients (Beck et al, 1985, 1990). Hence, although instruments such as Becks Hopelessness Scale may correctly identify those patients who subsequently die by suicide, but at the expense of also incorrectly identifying many who will not (Beck et al, 1985, 1990), our approach would not identify a large proportion of subsequent suicides.
Generalisability
The demographic characteristics and long-term outcomes of the patients
treated by the Hunter Area Toxicology Services are similar to some populations
in the UK (Hawton et al,
2003). The characteristics of the patients treated for repeated
self-harm and their subsequent long-term outcomes are also similar
(Zahl & Hawton, 2004). In
addition, the factors found to be predictive of suicide in our study (number
of tablets or different drugs ingested, and Glasgow Coma Scale score) can
easily be measured and recorded by non-psychiatrists. The GCS is widely used
internationally and would be expected to be part of the routine management of
a patient presenting with self-poisoning. Hence the results of the study can
be applied even to units where the clinicians have no special interest in
self-harm. If the rate of suicide is known in the population, the
individuals risk of subsequent suicide can be estimated using
likelihood ratios derived from this study
(Sacket, 1992).
Interventions to prevent subsequent suicide
People admitted to hospital for treatment of self-poisoning constitute a
population with a greatly increased risk of completed suicide
(Owens et al, 2002),
and within this group patients presenting on subsequent occasions with
escalating severity of poisoning may be at higher risk. Hence interventions
designed to prevent suicide or to reduce the repetition of self-poisoning
could be tested in this population. A few interventions have demonstrated a
decrease in rates of suicide a letter-writing intervention
(Motto & Bostrom, 2001)
or in repetition of self-harm: dialectical behaviour therapy, for
chronically parasuicidal women meeting criteria for borderline personality
disorder (Linehan et al,
1991); psychoanalytically informed partial hospitalisation, for
people with borderline personality disorder who harm themselves
(Bateman & Fonagy, 1999); a
brief interpersonal therapy intervention for hospital patients admitted for
deliberate self-harm (Guthrie et
al, 2001); and depot flupentixol
(Montgomery et al,
1979).
Although low cost interventions may be applied in all cases of deliberate self-poisoning, high-cost interventions may need to be restricted to high-risk subgroups. In order to apply such interventions it is first necessary to be able to identify patients at increased risk, without identifying an unnecessarily large number of people who are not at risk. Using the predictor variables identified from this study for those presenting with at least two episodes of self-poisoning would identify around half of those at risk (long-term) of death by suicide. To do this would require accurate data collection and the ability to compare sequential admissions. This process can be achieved using an electronic database, which could automatically identify patients at high risk of completed suicide. A model for such a system currently exists, where a clinical database could be used to inform psychiatry services of high risk patients (Whyte et al, 1997).
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Clinical Implications and Limitations |
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LIMITATIONS
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Received for publication March 24, 2004. Revision received September 9, 2004. Accepted for publication September 18, 2004.