Repeated self-poisoning: increasing severity of self-harm as a
predictor of subsequent suicide
Greg Carter, David M. Reith, Ian M. Whyte and Michelle McPherson
BJP 2005, 186:253-257.
Access the most recent version at DOI: 10.1192/bjp.186.3.253
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B R I T I S H J O U R N A L O F P S YC H I AT RY ( 2 0 0 5 ) , 1 8 6 , 2 5 3 ^ 2 5 7
Repeated self-poisoning: increasing severity of
self-harm as a predictor of subsequent suicide
GREG CARTER, DAVID M. REITH, IAN M. WHYTE and MICHELLE McPHERSON
Background Prediction of suicide risk
is difficult in clinical practice.
Aims To identify changes in clinical
presentation predictive of suicide in
patients treated for repeated episodes of
self-poisoning.
Method A nested case ^ control study
used the Hunter AreaToxicology 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 between15 January1987 and 31
December 2000.
Results There were 31cases, for which
93 controls were selected. Study variables
associated with an increased risk
riskof
of
subsequent suicide were an increase in the
number of drugs ingested (odds ratio 2.59,
95% CI1.48^4.51), an increase in the dose
ingested (OR1.33,95% CI1.01^1.76), an
increase in coma score (OR1.71,95% CI
1.11^2.66), a decrease in Glasgow Coma
Score (OR1.21,95% CI1.03^1.43) and an
increase in drug or alcohol misuse (OR
2.33,95% CI1.06^5.10).
Conclusions Patients who have
escalating severity of self-poisoning
episodes are at high risk of completed
suicide.
Declaration of interest
None.
Prediction of suicide for individuals has
proved to be elusive (Maris, 2002) and this
is usually attributed to the low base rate of
suicide (Addy, 1992). Suicide has multiple
risk factors and associated comorbidities,
such as mood disorders, personality disorders, substance misuse and poor physical
health. Although some tools for assessing
suicide risk may have a high sensitivity for
suicide, they also have low specificity and
limited usefulness in clinical practice (Powell
et al,
al, 2000; Eagles et al,
al, 2001). In some
patients suicidal ideation or suicidal behaviour may increase in severity over time.
The comparison of clinical characteristics
observed during a series of presentations
to clinical care may help to identify markers
of escalating self-harm, which might in turn
be predictive of subsequent suicide. We
have been unable to identify any previous
study of indicators of increasing severity
of self-harm prior to suicide. Our study
therefore aimed to identify changes in
clinical presentation predictive of suicide in
patients with repeated episodes of hospitaltreated self-poisoning.
METHOD
The study used a nested case–control
design; cases were patients who had been
treated for deliberate self-poisoning on more
than one occasion by the Hunter Area
Toxicology Service (Whyte et al,
al, 1997)
and had died by suicide. The Hunter Area
Toxicology Service is a regional toxicology
unit situated at the Newcastle Mater
Misericordiae Hospital in New South
Wales; it serves a population of around
350 000 people and is a tertiary referral
centre for a further 150 000. All poisoning
presentations to emergency departments in
the region are either admitted to the unit
or notified to the service and entered
prospectively into a clinical database.
Around 30% of patients presenting with
self-poisoning report previous episodes of
self-harm, and 18% had presented to the
Toxicology Service on more than one occasion; 38% of those who subsequently killed
themselves had presented to the service on
more than one occasion. Of patients who
presented to the service on more than one
occasion, 3% completed suicide within 5
years and 4% within 10 years.
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,
al, 1999).
Psychiatric diagnosis was made according
to DSM–III–R or DSM–IV (American
Psychiatry Association, 1987, 1994) and
confirmed at a weekly meeting. Individual
DSM diagnoses were then mapped to
DSM–IV 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,
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:
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).
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
2 53
CARTER E T AL
95% confidence intervals (CIs) were calculated using conditional logistic regression
for matched case–control 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,
al, 2004):
(a) indicators of medical seriousness: intensive care admission, length of stay in
intensive care, overall length of stay,
presence of seizures, Glasgow Coma
Scale (GCS; Teasdale & Jennet, 1974)
score on presentation and coma scale
(Plum & Posner, 1972) on presentation;
(b) indicators of serious intent: number of
tablets ingested, total dose ingested in
defined daily doses (Capella, 1997),
number of different medications
ingested, time from overdose to presentation and choice of poisoning method
(carbon monoxide v. medications);
(c) changes in drug and alcohol status
(medical staff ratings in the emergency
department);
(d) type of poisoning, psychiatric diagnosis
(new diagnosis on subsequent presentation) and new occurrence of involuntary
psychiatric admission or absconding.
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 case–control design.
RESULTS
(all from medicinal poisoning) and these
cases were excluded from the analysis. This
resulted in 31 cases, for which 93 controls
were selected (Table 1). For the cases, the
median time from last admission to suicide
was 305 days (range 4–2636). Nine of the
controls died during the study period: two
from cardiovascular
cardiovascular causes, one from
respiratory causes, one from endocrine
causes, one from hyposedative dependence,
one from opioid dependence, one from malignancy and one from accidental poisoning;
for one patient the cause of death was
unknown.
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.
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 0.59–0.88)
254
DISCUSSION
Methodological issues
Some of the limitations of our study include
the number of deaths in the control group,
the validity of the resident assessment of
drug and/or alcohol misuse and the difference in follow-up time between the cases
and controls. Some of the deaths in the
control group might have been misclassified
suicides; the resultant bias would be in the
direction of a negative result (type 2 error)
and hence would not affect the positive
findings of the study. However, other
potential risk factors such as length of stay
in hospital and discharge to an involuntary
psychiatric admission or absconding might
have been incorrectly found not to be
associated with suicide. The longer mean
follow-up time in the control group is expected, because the deaths of those in the
case group would have limited the followup period. The longer follow-up time in
the control group would also be expected
to lead to a negative result (type 2 error),
and would not have affected the positive
Table
Table 1 Characteristics of patients in the case and control groups at first presentation
Age, years: median (range)
Gender male/female, n/n
There were 34 patients who presented on
two or more occasions and subsequently
died by suicide. For three of these patients
death occurred during the last admission
(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 0.98–3.15), for a two or more increase
in number of drugs ingested was 3.60
(95% CI 1.03–12.53) and for a decrease
in GCS score of 2 or more was 5.36 (95%
CI 1.34–21.53).
Deliberate self-poisoning, n (%)
Died during study, n
Follow-up, days: median (range)
Cases (n
(n¼31)
31)
Controls (n
(n¼93)
93)
26 (14^70)
29 (12^81)
22/9
66/27
29 (94)
84 (90)
31
9
970 (170^4409)
2579 (18^5102)
R E P E AT E D S E L F - P OI S ONIN G
Table 2
Characteristics at first and last hospital-treated episodes and odds ratios for change from first to last for subsequent suicide
Characteristic
First admission
Last admission
OR (95% CI)
Change from first to last
Case
Control
Case
Control
5 (16.13)
16 (17.2)
6 (19.35)
14 (15.05)
44 (27.72^127)
32.5 (13.5^169)
NA
50 (2^226)
24 (2^308)
1.00 (1.0^1.01)
Indicators of medical seriousness
ICU admission, n (%)
Length of ICU stay, h: mean (range)
Length of hospital stay, h: mean (range)
Seizure, n (%)
43 (22.5^75.22) 23.41 (12.67^459.5)
41 (6^166)
50 (1^1222)
1.75 (0.55^5.56)
1 (3)
2 (2)
2 (6)
1 (1)
4.07 (0.34^48.23)
Decrease in GCS, score: mean (range)
14.3 (9^15)
13.5 (3^15)
13.2 (3^15)
14.1 (4^15)
1.21 (1.03^1.43)
Increase in coma score: mean (range)
0.56 (0^2)
0.96 (0^6)
1.03 (0^5)
0.78 (0^5)
1.71 (1.11^2.66)
2.59 (1.48^4.51)
Indicators of intent
Number of drugs ingested: mean (range)
2 (1^4)
2 (1^5)
2 (1^6)
2 (1^5)
Number of tablets ingested: mean (range)
24 (5^120)
36 (0^300)
40 (12^315)
30.5 (1^325)
Dose ingested1: mean (range)
0.75 (0.13^10)
1.26 (0^242)
Time to presentation: mean (range)
3.67 (0.53^27)
2.25 (0^72)
3 (0.83^22)
2.57 (0^26.58)
0.98 (0.93^1.03)
4 (12.9)
16 (17.2)
4 (12.9)
17 (18.2)
0.95 (0.39^2.33)
Ingestion of sedatives, n (%)
9 (29)
40 (43.5)
10 (32.3)
34 (36.6)
1.31 (0.66^2.58)
Carbon monoxide exposure, n (%)
2 (6.5)
1 (1.1)
0
1 (1.1)
Not performed
Insulin exposure, n (%)
0
2 (2.2)
1 (3.2)
2 (2.2)
Not performed
Ingestion of cardiac drug, n (%)
0
3 (3.2)
1 (3.2)
4 (4.3)
Not performed
452 (21^2003)
761 (3^4000)
1.0 (1.0^1.0)
Ingestion of antidepressants, n (%)
1.29 (0.25^334.28) 1.14 (0.07^16.33)
Time since previous admission, days: mean (range)
1.01 (1^1.02)
1.33 (1.01^1.76)
Medical officer ratings in the emergency department
Poisoning type: deliberate self-poisoning, n (%)
29 (93)
84 (90)
29 (93)
81 (87)
0.81 (0.21^3.02)
Rating of lifetime drug or alcohol misuse, n (%)
14 (45)
61 (66)
21 (68)
59 (63)
2.33 (1.06^5.10)
Involuntarypsychiatric admission or absconding, n (%)
5 (16)
20 (21)
10 (32)
18 (19)
2.18 (0.76^6.27)
Diagnosis of mood disorder, n (%)
5 (16)
20 (21)
5 (16)
24 (26)
0.60 (0.16^2.26)
Diagnosis of personality disorder, n (%)
4 (13)
14 (15)
5 (16)
20 (21)
1.0 (0.29^3.42)
Diagnosis of substance disorder, n (%)
2 (6)
26 (28)
8 (26)
38 (41)
0.73 (0.27^1.99)
Diagnosis of psychosis, n (%)
3 (10)
6 (6)
4 (13)
9 (10)
0.75 (0.08^6.76)
Psychiatric diagnosis and discharge status
GCS, Glasgow Coma Scale; ICU, intensive care unit; NA, not available.
1. Number of defined daily doses.
T
Table
able 3
Sensitivity and specificity (at optimal cut-off points) of changes in clinical characteristics for predicting suicide1
Clinical characteristic
Sensitivity (%)
Specificity (%)
Decrease in GCS score of 2 or more
24 (16^32)
93 (88^98)
Increase in coma score of 2 or more
20 (12^28)
93 (89^98)
Indicators of medical seriousness
Indicators of intent
Two or more increase in number of drugs ingested
22 (15^30)
94 (91^98)
70 or more increase in the number of tablets ingested
50 or more increase in DDDs ingested
37 (26^48)
21 (12^30)
91 (85^98)
100 (100^100)
29 (21^37)
86 (80^92)
Psychiatric diagnosis and drug misuse
New rating of lifetime drug or alcohol misuse
Combined scores
Two or more increase in number of drugs ingested and/or decrease in GCS score of 2 or more
40 (30^50)
91 (85^96)
70 or more increase in the number of tablets ingested and/or decrease in GCS score of 2 or more
53 (41^65)
87 (79^95)
70 or more increase in the number of tablets ingested and/or deterioration in current DA status
47 (36^58)
82 (73^90)
70 or more increase in the number of tablets ingested and/or deterioration in current DA status and/or
decrease in GCS score of 2 or more
47 (34^59)
76 (66^86)
DA, drug and alcohol; DDDs, defined daily doses; GCS, Glasgow Coma Scale.
1. 95% confidence intervals.
255
CARTER E T AL
Generalisability
Fig. 1 Receiver operating characteristic curve for change in the number of tablets ingested (area under curve
0.7355).
findings of the present study. The medical
officer’s rating of lifetime drug or alcohol
misuse, when previously compared with
the gold standard of DSM–IV (substance
abuse) as rated by clinical psychiatric assessment, had a sensitivity of 91% and a specificity of 60% (Dawson, 2000). The medical
officer’s rating of lifetime drug or alcohol
misuse is probably a broader measure of
substance exposure or misuse than the
DSM diagnosis of substance- related disorder, which was also used in this study.
Hence, the medical officer’s assessment of
lifetime substance misuse, although readily
performed, does not correspond to the
DSM–IV criteria. The nested case–control
design used in our study, unlike some other
case–control designs, was not affected by
ascertainment or recall bias because the
Hunter Area Toxicology Service treats all
self-poisoning patients from the region
and all of the exposure variables were
collected prospectively.
Risk factors for suicide
after self-harm
People who deliberately harm themselves
have an increased risk of suicide (Owens et
al,
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,
al, 2001; Beautrais, 2003). Specifically following deliberate self-poisoning,
256
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,
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 Beck’s Hopelessness
Scale: 51% for hospitalised patients with
suicidal ideation and 41% for psychiatric
out-patients (Beck et al,
al, 1985, 1990). However, the sensitivity of Beck’s Hopelessness
Scale was greater: 91% for hospitalised
patients with suicidal ideation and 94%
for psychiatric out-patients (Beck et al,
al,
1985, 1990). Hence, although instruments
such as Beck’s 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,
al, 1985, 1990), our
approach would not identify a large
proportion of subsequent suicides.
The demographic characteristics and longterm outcomes of the patients treated by
the Hunter Area Toxicology Services are
similar to some populations in the UK
(Hawton et al,
al, 2003). The characteristics
of the patients treated for repeated selfharm 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 individual’s
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,
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,
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,
al, 2001); and depot flupentixol
(Montgomery et al,
al, 1979).
Although low cost interventions may
be applied in all cases of deliberate selfpoisoning, 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
R E P E AT E D S E L F - P OI S ONIN G
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 selfpoisoning 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,
al, 1997).
CLINICAL IMPLICATIONS
& Patients whose repeated self-poisoning episodes are of escalating severity are at
increased risk of completed suicide.
These patients may warrant additional short-term and long-term attention from
clinical services in order to reduce their long-term risk of subsequent suicide.
&
Any long-term system of monitoring and treating self-poisoning patients might
include these markers of increased risk.
&
LIMITATIONS
&
The resident assessment of drug and/or alcohol misuse differs from the DSM^IV
substance abuse criteria.
&
&
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