Introduction

Nonsuicidal self-injury (NSSI) and suicide attempts (SAs) among youths are major public health concerns. NSSI refers to behaviors related to self-inflicted injury without any intent to die, such as nonsuicidal cutting, burning, and scratching. SA refers to self-inflicted injury with at least some intent to die (Nock, 2010). Both NSSI and suicidal behavior disorders were introduced in the latest version of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5; American Psychiatric Association, 2013) as conditions for further study. Although many have advocated for the separation of these diagnostic entities (Butler & Malone, 2018; Huang, Ribeiro, & Franklin, 2020; Oquendo & Baca-Garcia, 2014; Zetterqvist, 2015), there is an ongoing debate whether NSSI and SA are distinct behaviors, and if it is possible to separate them (Grandclerc, Labrouhe, Spodenkiewicz, Lachal, & Moro, 2016; Huang et al., 2020; Kapur, Cooper, O’Connor, & Hawton, 2013).

Self-injury, regardless of intent, is one of the strongest predictors for future self-injury/SA (Castellví et al., 2017; Ribeiro et al., 2016) and has also been reliably linked to substance use disorder (Beckman et al., 2016; Moran et al., 2015; Ohlis et al., 2020) and a higher frequency of psychiatric inpatient care (Beckman et al., 2016; Ohlis et al., 2020). Both substance use disorder and psychiatric inpatient care have been associated with elevated risks of a range of fatal and nonfatal adverse outcomes, including death, self-injury, and violent criminality (Chai et al., 2020; King et al., 2019; Olfson et al., 2018; Walter et al., 2017, 2019).

To our knowledge, only two longitudinal studies have compared differences in outcomes between youths with NSSI and SA, compared with youths without these problems (Bjureberg et al., 2019; Mars, Heron, Crane, Hawton, Lewis, et al., 2014). In a population-based community cohort, Mars, Heron, Crane, Hawton, Kidger, et al. (2014) found that youths who reported either NSSI or SA at age 16 were at greater risk of mental health problems in young adulthood, compared to youths who did not report any self-injurious behaviors. Furthermore, these associations were generally stronger for youths with SA than NSSI. These findings indicate that it may be meaningful to differentiate between NSSI and SA, and the fact that both behaviors were associated with poor outcomes highlight the critical importance of early identification, prevention, and treatment of these conditions. However, Mars, Heron, Crane, Hawton, Kidger, et al. (2014) study relied on self-reports to measure NSSI and SA, as well as several of the included outcomes. Notably, self-reports of mental health problems are associated with a number of potential biases; not least because the same person reports the exposure and the outcome. Also, they tend to underestimate the occurrence of mental disorders and maladaptive behaviors, and the most severely affected participants are more likely to drop out from follow-up in longitudinal studies (Copeland, Shanahan, Costello, & Angold, 2011; Moffitt et al., 2010; Rothman, 2012; Takayanagi et al., 2014). Although participants and measurements derived from registries may introduce other type of biases, they are not prone to reporter bias, and participants are characterized by help-seeking behavior and, for those who are assigned with a psychiatric diagnoses, phenotypic severity. Furthermore, register studies possess demographic features that are representative for their population (Copeland et al., 2011; Moffitt et al., 2010; Rothman, 2012; Takayanagi et al., 2014). These parameters are crucial in clinical and health economic considerations (Takayanagi et al., 2014). Thus, register-based data may be an important source of information to complement studies based on self-reports.

Our group recently replicated several of Mars, Heron, Crane, Hawton, Kidger, et al. (2014) findings based on data from a Swedish regional clinical register, using records of youths with self-injury with and without suicidality, and linked these to register-based outcomes (Bjureberg et al., 2019). However, in Bjureberg et al. (2019), we lacked the possibility to differentiate between suicidal ideation and SA, and just as Mars, Heron, Crane, Hawton, Kidger, et al. (2014), NSSI and SA was defined as present or absent at the baseline of the study, and then used as predictors for adverse outcomes years later. Considering that suicidal intention may vary over time, research into these behaviors may benefit from the use of time-to-event data with several points of measurement, as NSSI and SA may be better understood as dynamic, rather than static, phenomena (Huang et al., 2020; Kapur et al., 2013). Taken together, there is a need of studies including repeated observations of both NSSI and SA to provide clinicians with more accurate data on which to base their risk assessments, at the time they meet their patients.

The aim of this study was to assess adverse clinical outcomes in a sample of clinically assessed youths with NSSI and/or SA measured as time-varying covariates, as compared with youths without NSSI or SA. To address this aim, we evaluated three groups defined as follows: (a) presented with NSSI but no indication of SA; (b) presented with SA but no indication of NSSI; and (c) presented with both NSSI and SA. Ethical approval was granted by the Stockholm Regional Ethics Committee (2013/862:31/5).

Methods Sample

A total of 17,192 youths (48.6% females) between the ages of 51. and 17 sought care at the child and adolescent mental health services (CAMHS) in Stockholm County Council between December, 2011 and December, 2013. The clinical care that the patients received could include everything from a single assessment to extensive medical and psychosocial treatments. Of these, 1,855 (12.9%; of which 74.6% were female) had undergone one or more registered assessments (m = 1.2; SD = 0.5) of NSSI and SA during their contact with CAMHS (see Figure S1 for a participant flow diagram).

Assessments of NSSI and SA

Medical doctors at CAMHS in Stockholm are instructed to assess NSSI and SA in youths that may be at risk of either of these behaviors. Any assessment of NSSI, as well as SA, is then recorded in the electronic charts, in which the presence and frequency of NSSI and SA are assessed separately (coded as 0 or 1). In the electronic chart, NSSI is defined in verbatim as ‘the direct and deliberate self-inflicted destruction of body tissue without suicidal intent’. This definition is accompanied with the following instruction: ‘if suicidal intent is unclear, the behavior should be categorized as a SA. SA is defined as ‘the non-fatal life threatening or seemingly life threatening behavior (an attempt to jeopardize one’s life or make the impression of such intent)’. This definition is followed by the instruction that ‘direct and deliberate self-injury with unclear intent should be categorized as SA’.

Outcome measurements

The outcome measurements were derived from a linkage of several Swedish national registers. The National Patient Register (Ludvigsson et al., 2011) covers psychiatric in- and outpatient care, and includes physician-assigned, dated diagnoses according to the Tenth version of the International Classification of Diseases (ICD-10; American Psychiatric Organization, 1992). Self-injury was defined as an ICD-10 diagnosis of X60-84 or Y10-34 (including NSSI and/or SA, alcohol misuse and/or substance use as F10-19, not including F17, and psychiatric inpatient care as an inpatient episode due to any mental disorder in the ICD-10. Self-inflicted harm of undetermined intent was included to avoid underestimation of self-injury Neeleman & Wessely, 1997; Runeson et al. (2010).

Covariates

Sex and the number of clinical assessments per individual were included as covariates, as increasing numbers of clinical assessments may be associated with an increased likelihood of being positively assessed with NSSI and SA, as well as a potentially elevated risk of the outcomes, as the presence of more assessments may index more problems in general.

Statistical analysis

Statistical analyses were performed in Stata version 14.2 (StataCorp, College Station, TX). Hazard ratios (HRs) with 95% confidence intervals (CIs) for the outcomes were estimated with Cox regressions. End of follow-up was either the outcome event or censoring at end of data coverage, whichever happened first. In the Cox regression model, the underlying time-scale was time since first clinical assessment of NSSI or SA. To take potential cross-over from NSSI to SA into account, NSSI and SA were included in the model as time-varying covariates, meaning that an individual could be positively assessed with NSSI at one time point, and SA at another time point. We then ran two additional analyses for all outcomes; first by including sex as a covariate, second by adding the number of assessments to the model. To check if participants at the young end of the sample had impacted the overall findings, we reran all analyses excluding participants under the age of 10 years. The proportional hazards assumption was not violated in any analysis (tested with Stata’s estat phtest, which tests the proportional hazards assumption on the basis of Schoenfeld residuals).

Results

Descriptive statistics are shown in Table 1. Participants presented with a variety of mental disorders during the study period, most commonly anxiety and depressive disorders that were prevalent in all groups (see Table S1 for ICD-10 codes). Mean follow-up time was 7.0 months. A total of 10.0% of youths with a positive assessment of NSSI were subsequently assigned a diagnosis of self-injury (i.e., ICD-10 X60-84 or Y10-34; see Table S2 for a frequency table of types of self-injury), 5.5% received a later alcohol and/or substance abuse disorder, and 16.6% were subsequently admitted to psychiatric inpatient care. One-fifth of youths with a positive assessment of SA were subsequently assigned with a diagnosis of self-injury, 7.6% received an alcohol and/or substance abuse disorder, and 27.6% were admitted to psychiatric inpatient care. Finally, 21.3% of adolescents who were assessed to have engaged in both behaviors (NSSI and SA) were subsequently assigned with a diagnosis of self-injury, 8.5% were diagnosed with an alcohol/substance abuse disorder, and 45.8% were later admitted to psychiatric inpatient care.

Table 1. Demographic and descriptive characteristics of the study cohort, by nonsuicidal self-injury (NSSI), suicide attempts (SA), and both NSSI and SA status Total Ever NSSI (not SA) Ever SA (not NSSI) NSSI+SA No NSSI or SA N 1,855 633 89 125 1,008 Female sex, n (%) 1,368 (73.7) 540 (85.3) 68 (76.4) 104 (83.2) 656 (65.1) Mean age (SD) in years at start of follow-up 15.5 (1.8) 15.5 (1.6) 15.8 (1.6) 15.8 (1.6) 15.4 (2.0) Mean age (SD) in years at end of follow-up 16.4 (1.8) 16.3 (1.6) 16.7 (1.5) 16.8 (1.5) 16.3 (1.9) Mean number (SD) of clinical assessments 1.8 (2.0) 2.2 (2.1) 1.7 (1.2) 4.2 (4.7) 1.3 (0.7) Mental disordersa Affective disorder 657 (35.4%) 256 (40.4%) 31 (34.8%) 71 (56.8%) 299 (29.7%) Anxiety disorders 850 (45.8%) 329 (52.0%) 53 (59.6%) 93 (74.4%) 375 (37.2%) Eating disorders 145 (7.8%) 72 (11.4%) 8 (9.0%) 10 (8.0%) 55 (5.5%) Psychotic disorders 32 (1.7%) 4 (0.6%) 2 (2.2%) 4 (3.2%) 22 (2.2%) Personality disorders 55 (3.0%) 28 (4.4%) 3 (3.4%) 13 (10.4%) 11 (1.1%) NSSI, nonsuicidal self-injury; SA, suicide attempts. In this table, the ‘NSSI+SA’ category includes both those who have been rated to have NSSI an SA at one rating occasion and those who have had NSSI and SA at separate rating occasions. a See Table S1 for ICD-10 codes.

Results from the Cox regressions are presented in Table 2. The crude HRs for youths with a positive assessment of NSSI compared with youths with negative assessments of NSSI or SA were 2.3, 95% CI [1.6, 3.4] for subsequent self-injury diagnosis, 1.4 [0.9, 2.1] for alcohol/substance abuse disorder, and 1.7 [1.3, 2.3] for inpatient psychiatric care. The crude HR for youths with a positive assessment of SA compared with youths with no NSSI/SA were 5.5 [2.4, 12.6] for subsequent self-injury diagnosis, 2.0 [0.9, 4.4] for alcohol/substance use disorder, and 2.6 [1.5, 4.5] for inpatient psychiatric care. Finally, for adolescents who were assessed to have engaged in both behaviors (NSSI and SA), the crude HR, compared to youths without NSSI/SA, were 4.1 [2.0, 8.3] for self-injury diagnosis, 2.0 [1.1, 4.1] for alcohol/substance abuse disorder, and 5.0 [3.1, 7.9] for psychiatric inpatient care. The magnitude of the effect sizes remained virtually unchanged in the adjusted analyses (Table 2).

Table 2. Subsequent adverse outcomes in youths (N = 1,855) with clinically assessed nonsuicidal self-injury (NSSI), suicide attempts (SA), or both NSSI and SA (NSSI+SA), compared with youths without NSSI SA # (%) HR (CI) HR (CI) HR (CI) Crude Adjusteda Adjustedb Self-injuryc NSSI 59 (10.0) 2.3 (1.6, 3.4) 2.1 (1.4, 3.2) 2.1 (1.4, 3.1) SA 9 (20.5) 5.5 (2.4, 12.6) 5.6 (2.4, 12.8) 5.2 (2.4, 12.2) NSSI+SA 10 (21.3) 4.1 (2.0, 8.3) 4.4 (2.2, 9.0) 4.2 (1.9, 9.5) No NSSI or SA 48 (4.4) Alcohol/substance use disorderd NSSI 35 (5.5) 1.4 (0.9, 2.1) 1.4 (0.9, 2.3) 1.4 (0.9, 2.2) SA 7 (7.6) 2.0 (0.9, 4.4) 2.0 (0.9, 4.4) 1.9 (0.9, 4.3) NSSI+SA 9 (8.5) 2.0 (1.1, 4.1) 2.1 (1.1, 4.2) 1.8 (0.9, 3.7) No NSSI or SA 40 (3.2) Psychiatric inpatient caree NSSI 95 (16.6) 1.3 (1.0, 1.7) 1.3 (1.0, 1.7) 1.2 (0.9, 1.7) SA 22 (27.6) 2.6 (1.5, 4.5) 2.6 (1.5, 4.6) 2.6 (1.5, 4.5) NSSI+SA 33 (45.8) 5.0 (3.1, 7.9) 5.0 (3.1, 7.9) 4.8 (3.0, 7.9) No NSSI or SA 141 (13.1) Risk estimates are hazard ratios (HRs) with 95% confidence intervals (CIs). a Adjusted for sex. b Adjusted for sex and number of clinical assessments. c 187 participants were excluded from the analyses because they had experienced the outcome before the date of their first clinical assessment. d 131 participants were excluded from the analyses because they had experienced the outcome before the date of their first clinical assessment. e 241 participants were excluded from the analyses because they had experienced the outcome before the date of their first clinical assessment.

Results from the additional statistical analyses that were restricted to participants over the age of 10 years at the first clinical assessment were similar to those including all participants (see Table S3).

For completeness, NSSI was also directly compared to SA and NSSI+SA (see Table S4). Patient with NSSI had statistically significantly lower risk for subsequent self-injury diagnosis and psychiatric inpatient care compared to patients with SA (OR range 0.4–0.7) and patients with NSSI+SA (OR range 0.2–0.6). Although the point estimates for alcohol/substance use disorder followed a similar pattern with lower HR for the NSSI group compared to SA and NSSI+SA, they were not statistically significant.

Discussion

In this longitudinal cohort study, we found that both youths with NSSI and SA—separately and combined—had elevated risks of being diagnosed with ICD-10 diagnosis of subsequent self-injury diagnosis, alcohol misuse, and/or substance use disorder, and being admitted to psychiatric inpatient care. These findings are in line with previous research (Andover, Morris, Wren, & Bruzzese, 2012; Beckman et al., 2016; Borschmann et al., 2017; Geulayov et al., 2016; Hawton et al., 2003; Mars, Heron, Crane, Hawton, Lewis, et al., 2014; Mars et al., 2019; Ohlis et al., 2020). Our results further indicate that SA (on its own or when accompanied by NSSI) may be associated with greater risks for some adverse outcomes than only NSSI, further corroborating prior results from community-based samples (Mars, Heron, Crane, Hawton, Kidger, et al., 2014), also in a clinical cohort. These findings suggest that suicidality is an important—although not necessary—factor for increased risks for subsequent adverse outcomes in youths with self-injury. Future studies should further assess if youths with both NSSI and SA are at even greater risk of adverse outcomes, which was the case in the current study with regard to psychiatric inpatient care.

There still is no consensus regarding the nomenclature for self-injury and SA (Asarnow & Mehlum, 2019), and researchers debate if NSSI represents a distinct construct or if it rather is part of a continuum of self-injurious behaviors, including suicidal behavior, and if it is meaningful, or even possible to separate these two phenotypes (Kapur et al., 2013). As there was indication that SAs (alone and when accompanied by NSSI) were associated with greater risks for adverse clinical outcomes, our findings suggest that it may be useful for adequate risk assessment and treatment planning to separate NSSI from SA, which has important implications for the potential inclusion of the NSSI and suicidal behavior disorders in future versions of the DSM (American Psychiatric Association, 2013). Moreover, our results underscore that NSSI and SA not only predicted subsequent self-injury (Asarnow et al., 2011; Guan, Fox, & Prinstein, 2012; Wilkinson, Kelvin, Roberts, Dubicka, & Goodyer, 2011) but also diagnosed alcohol misuse and/or substance use disorder. Thus, risk assessments and interventions for youths with NSSI or SA need to have a broad focus considering the increased risk of development of alcohol misuse and/or substance use disorder, and not only focus on suicide prevention—particularly considering that treatment of alcohol and/or substance use disorder may be important to prevent suicide (Chai et al., 2020; Esang & Ahmed, 2018; King et al., 2019). Moreover, given that inpatient care results from patient severity (patient evaluated as unsafe to return home), it is not surprising that admission to psychiatric inpatient care is generally a risk marker for a range of adverse outcomes such as death, suicide, and committing a violent crime (Walter et al., 2017, 2019). Thus, the high risks for being admitted to psychiatric inpatient care for the patients in the current study, among both youths with NSSI and SA but particularly in the NSSI+SA group, suggest that youth patients who engage in both NSSI and SA have elevated risks for a range of adverse outcomes beyond the adversities examined in this study. In addition to being a general risk marker, possibly as a result of confounding by indication, inpatient care may also have detrimental effects contributing to self-injury risk (Carroll et al., 2016; Hjorthøj, Madsen, Agerbo, & Nordentoft, 2014; Ougrin et al., 2018; Reavey et al., 2017), potentially due to exposure to other patients with self-injury and reinforcement contingencies (e.g., negative reinforcement by avoidance of negative experiences at home and in school, and positive reinforcement by increased care and attention following self-injurious behavior). In line with suggestions for future research offered in a recent meta-analysis of psychosocial interventions for self-injurious behaviors in adolescents (Kothgassner, Robinson, Goreis, Ougrin, & Plener, 2020), our results suggest that the development of effective and safe inpatient care (or alternatives thereof) for patients with self-injurious behaviors should be considered a research priority.

It is notable that this study detected statistically significant risk of adverse outcomes using a relatively short follow-up period of 7 months, which is substantially shorter than in the studies by Mars, Heron, Crane, Hawton, Kidger, et al. (2014) and Bjureberg et al. (2019), where patients were followed for about 3 years. The findings in this study indicate that detection of youth self-injury could signal high risk of adverse outcomes within short time intervals, underscoring the importance of targeted prevention immediately after disclosure. Finally, in concert with prior research (Bjureberg et al., 2019; Mars, Heron, Crane, Hawton, Lewis, et al., 2014; Moran et al., 2012), the majority of youths with NSSI or SA were not diagnosed with self-injury during follow-up (see Table 2). Longitudinal studies that pin-point resilience or health promoting factors that cause some youths to quit harming themselves are imperative for the improvement of prevention and treatment interventions for youths with these problems.

This study has several strengths. To our knowledge, it is the first study comparing risks of subsequent adverse clinical outcomes of youth NSSI and SA where the analyses allowed these behaviors to vary over time, rather than only considering baseline assessments of the exposure to NSSI or SA. By doing so, findings from this study inform clinicians about the risk of clinical outcomes by their status at the time they assess their patients, depending on whether they present with NSSI, SA, or both, in contrast to prior studies showing an excess risk of substance use and recurrent self-injury at the age of 18 and 21 in individuals who reported NSSI at the age of 16 (Mars, Heron, Crane, Hawton, Lewis, et al., 2014), and thus not taking into account that these processes are dynamic (Huang et al., 2020). Moreover, this study was also the first to utilize clinical assessments of NSSI and SA, rather than self-reports, and thus mastered some potential biases related to self-reported mental health problems in earlier studies.

This study also has important limitations that should be considered when interpreting the results; only a smaller proportion of the youths who had contact with CAMHS during the observation period were either subject to the clinical assessment of NSSI and SA or the assessments were not registered in the digital charts. The study participants were thus likely selected on one or more unobservable factors, such as type of CAMHS unit (e.g., emergency ward, outpatient clinics) and varying compliance among clinician to register assessments in the designated space in the digital chart. This could potentially have introduced selection bias such as confounding by indication, which may have led to an underestimation of the difference between patients with any of the three exposures (NSSI, SA, NSSI+SA) and patients with no NSSI or SA. It is worth to note, however, that clinical assessments of NSSI and SA are routine at CAMHS units, which may have mitigated this potential selection effect. Moreover, the statistical power was limited in some situations, which affected the CIs around the point estimates. Another limitation is the absence of information on suicidal ideation and severity of self-injury. Some youths presenting with NSSI may also show suicidal ideation; these youth may have outcomes more similar to youth presenting with SA. However, the registry data do not allow these questions to be addressed and should be considered in future work. Moreover, the registries do not include complete information on type of treatment received during their CAHMS contact. Thus, we do not know to what extent treatment delivery affected the results. Testing potential effects of psychosocial and pharmacological treatments on the trajectories should be explored in future studies. It should also be mentioned that although there are advantages with clinical assessments of NSSI and SA, youth are more likely to report self-injurious behaviors on questionnaires, rather than when asked (Ougrin & Boege, 2013). This may have resulted in false negatives, which possibly lead to an underestimation of the differences between the three exposure groups and clinical controls. Further, although the sample included children as young as 5 years old, the mean age of the sample at start of follow-up was 15.5 years with little variance, which limits the generalizability of the present results for the youngest children. Further, race or ethnicity was not reported because these variables were not available in the dataset. Finally, this study does not provide evidence on different risk factors for NSSI or SA. Future research should study familial and individual candidate risk factors such as emotion dysregulation (Kim et al., 2020), impulsivity (Liu, Trout, Hernandez, Cheek, & Gerlus, 2017), and victimization (Baldwin et al., 2019) that may suggest different pathways to NSSI and SA.

Conclusions

Youths who were positively assessed with NSSI, SA, or both had substantially elevated risks of subsequent adverse clinical outcomes, when compared with youths who were negatively assessed with NSSI or SA, also after adjustment for sex, and number of assessments. SA generally conferred higher risks of the outcomes than NSSI alone, and youths positively assessed with both NSSI and SA had five times the HR of being admitted to psychiatric inpatient care, an indicator of acute mental health needs and indicator of subsequent adverse events, a finding that warrants further study. Early interventions for youths with NSSI or SA should not exclusively focus on suicide prevention, but also consider the risk of subsequent alcohol/substance use disorder. Given the increased risk of inpatient care and the complex associations between inpatient care and subsequent risk of a range of adverse outcomes, particularly for self-injuring youth, ensuring that inpatient care is an effective and safe treatment alternative (or developing alternatives thereof) for this population is a research priority.

Acknowledgments This research was supported by the Swedish Research Foundation (Grant no. 2017-01506). J.B. was supported by Knut and Alice Wallenberg Foundation (Grant no. KAW 2018.0426). The authors have declared that they have no competing or potential conflicts of interest. Key pointsSelf-injury is common among youth and associated with adverse clinical outcomes. Longitudinal research with repeated measurements that cleary differentiate between nonsuicidal self-injufry (NSSI) and suicide attempts (SA) are imperative to better understand their respective relevance in clinical samples. This study shows that youth with NSSI and/or SA have increased risks of adverse clinical outcomes, with the excess risks being more pronounced for SA on its own, or when accompanied by NSSI. The risk for psychiatric inpatient care was particularly high in the group with both NSSI and SA. SA, in particular when accompanied by NSSI, could be a risk marker of increased risks of adversities among self-injuring youth. Interventions should not exclusively focus on suicide prevention, but also consider the risk of alcohol/substance use disorder. Note 1 5 years was selected as a lower threshold given data showing that nonsuicidal self-injury and suicide attempts can occur in very young children (Luby et al., 2019) and research suggesting that children begin to conceptualize death as a biological event between the ages of 5 and 6 years (Slaughter, 2005). Filename Description jcpp13544-sup-0001-Supinfo.docxWord document, 39.9 KB

Figure S1. Participant flow through the study. CAMHS = child and adolescent mental health services.

Table S1. International Classification of Diseases (ICD-10) codes for groups of mental disorders.

Table S2. Frequency of types of self-injury.

Table S3. Subsequent adverse outcomes in youth between the ages of 10 and 17 at start of follow-up with clinically assessed nonsuicidal self-injury (NSSI), suicide attempts (SAs), or NSSI and SA (NSSI+SA), compared with youths without NSSI or SA.

Table S4. Subsequent adverse outcomes in youths with clinically assessed nonsuicidal self-injury (NSSI), compared with youths with SAs, and youths with both NSSI and SA (NSSI+SA).

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