Table 2.

Description of included studies

Study	Title	Country of origin	Study design	Age group	Participants	Results	Quality assessment
Cappelli et al. [17]	Transitioning youth into adult mental health and addiction services: An outcome evaluation of the youth transition project	Canada	Service evaluation	Young people (YP) between ages of 16 and 24	215 Young people (YP) accessing CAMHS who were referred to the transition programme	Young people (YP) who transitioned were more likely to have a higher score on a measure of antisocial behaviour (x2(1,59) = 3.84, p = 0.05) or have an anxiety disorder (x2(1,199) = 4.05, p = 0.044) than those who engaged with services. YP who transitioned as opposed to remaining on the waiting list had a higher number of visits to the emergency department (x2(1,115) = 4.76, p = 0.029) and reported more unmet needs relating to psychological distress (x2(3,106) = 10.98, p = 0.012). YP who remained on the waiting list were more likely to have oppositional defiant disorder (x2(1,200) = 7.64, p = 0.006) or ADHD (x2(1,200) = 4.83, p = 0.028)	Good
Islam et al. [18]	Mind how you cross the gap! Outcomes for young people who failed to make the transition from child to adult services	England	Retrospective case note analysis	YP who reached transition boundary during 12 month study period and had not been transitioned to AMHS after reaching the CAMHS age boundary	64 YP who had mental health needs, but were not transitioned to AMHS	The majority of YP who did not transition to AMHS were those with a diagnosis of an emotional or neurotic disorder (48.4%). The next most common diagnostic group who did not transition were those with a neurodevelopmental disorder (23.4%)	Good
McNicholas et al. [5]	Who is in the transition gap? Transition from CAMHS to AMHS in the Republic of Ireland	Republic of Ireland	Retrospective case note analysis	Cases included if YP were open to the service when they reached the upper age limit of that service in the 12 month study period	62 YP who crossed CAMHS transition boundary	Several of the YP with an ongoing mental health need (n = 47) were not referred to AMHS (45%). Refusal by the YP or their parent/carer was also a common reason for non-referral (23%). 32% of YP were referred to AMHS, with YP more likely to make the transition if they had a diagnosis of psychosis (x2(2,45) = 8.96, p = 0.02, V = 0.45). In contrast, YP with a diagnosis of ADHD were most likely to refuse the referral to AMHS (x2(2,45) = 6.81, p = 0.01, V = 0.44)	Good
Memarzia et al. [16]	Adolescents leaving mental health or social care services: predictors of mental health and psychosocial outcomes 1 year later	England	Longitudinal cohort study	YP aged 17–18 facing transition	26 YP who were about to leave CAMHS and 27 looked after children	Of the YP who left CAMHS, the majority (82%) were discharged to their GP, whilst 14% were referred to AMHS. Mental health outcomes were recorded, but could not be extracted for the CAMHS leavers, as data were grouped with the whole cohort	Good
Moosa and Sandhu [19]	Transition from children’s to adult services for patients with ADHD: a model of care	England	Service evaluation	Adolescents 15 or over with a diagnosis of ADHD who were open to CAMHS	247 YP with ADHD who were 15 or older in CAMHS	Before this scheme was introduced, 134 YP remained at CAMHS after they had reached the upper age limit of the service, which was reduced to 14 following its implementation. The referral rate to AMHS increased from 67 to 95% after the new initiative	Good
Ogundele [2]	Transitional care to adult ADHD services in a North West England District	England	Retrospective case note analysis	Adolescents with ADHD from childhood who were eligible for transition to AMHS, who reached 16 years old during study period	104 YP who were eligible for transition to AMHS	65% of YP were discharged from paediatric services without referral, often due to disengagement or self-discharge. 15% of YP were referred to an AMHS, and 18% to a CAMHS service. Of these YP referred to another service, 32% were discharged within the following 2 years	Poor
Paul et al. [3]	Transfers and transitions between child and adult mental health services	England	Retrospective case note analysis	YP who reached transition boundary during 12 month study period	154 YP who crossed transition boundary	Of the 131 YP with an ongoing clinical need, 102 were referred to AMHS and 90 were accepted. The most common reasons for non-referral were the CAMHS clinicians thinking AMHS would not accept the referral or not having an appropriate service to refer to, delayed referral, or refusal by the YP or their parent/carer	Good
Perera et al. [22]	Determinants of transition from child and adolescent to adult mental health services: A Western Australian Pilot Study	Australia	Retrospective case note analysis	CAMHS closed cases from 01/06/04 to 30/06/13 if YP were within transition age (16–21)	245 YP discharged from CAMHS at transition boundary	Four main transition pathways from CAMHS were identified: not referred, directly referred to AMHS, delayed referral to AMHS, and referred but not accepted. CAMHS diagnosis was associated with the likelihood of engagement at AMHS (x2(2) = 10.99, p < 0.001). In particular, YP with a neurotic disorder were less likely to be engaged at AMHS than those with a mood or other types of disorder (all zs ≥ 2.25, ps ≤ 0.01)	Good
Reale et al. [24]	Transition to adult mental health services for young people with attention-deficit/hyperactivity disorder in Italy: parent’s and clinician’s experiences	Italy	Qualitative questionnaire study	Parents of adolescents with ADHD who reached adulthood—identified through mailing list of support group	Parents and clinicians of YP with ADHD representing 24 young adults	Results showed that the most common outcome following transition from the children’s service was no ongoing care (38%), excluding the YP who had been discharged because of good health (12%). No YP had been referred to the adult service from their children’s service, although 21% were receiving care in a public adult mental health service and 17% by a private specialist. A further 12% of YP continued to receive care at the children’s service after crossing the transition boundary	Poor
Schandrin et al. [21]	Transition from child to adult mental health services: a French retrospective study	France	Retrospective case note analysis	Every patient whose transition from CAMHS to AMHS was initiated at a hospital during the 2 year study period	31 YP who transition had been initiated	Transition was completed in 90% of cases; however, YP often experienced discontinuity of care during their transition with an average gap of 3 months of no care between the services. At 3 months following transition to AMHS, 84% were actively engaged, although this fell to 45% at one to 3 years later	Poor
Singh et al. [4]	Process, outcome and experience of transition from child to adult mental healthcare: multiperspective study	England	Retrospective case note analysis	See Paul et al. [3]	154 YP who crossed transition boundary	YP were more likely to be referred to AMHS if they had been admitted under the Mental Health Act (OR 5.0; 95% CI clustered 1.6–15.5; p = 0.01), had a severe and enduring mental illness (OR 2.82; 95% CI clustered 0.8–9.6; p = 0.01), were on medication at the time of transition (OR 7.85; 95% CI clustered 1.5–40.9; p = 0.01), or had a comorbidity (OR 2.36; 95% CI clustered 1.7–3.4; p < 0.01). YP with emerging personality disorder were reported to be more likely to fall through the gap; however, the numbers were too small to draw statistically significant conclusions	Good
Stagi et al. [23]	Continuity of care from child and adolescent to adult mental health services: evidence from a regional survey in Northern Italy	Italy	Retrospective case note analysis	YP aged 16 or older listed in a health database as having attended CAMHS in a 3 year period. Received formal diagnosis	8239 YP who crossed the CAMHS transition boundary	Over the 4 year study period, 19.4% of YP were transferred to AMHS. YP were more likely to make this transition if they had a diagnosis of schizophrenia or related disorders (OR 3.92; 95% CI 2.17–7.08), a personality disorder (OR 2.69; 95% CI 1.89–3.83) or a pervasive developmental disorder (OR 2.13; 95% CI 1.51–2.99). Of the 2771 YP referred to AMHS, 580 were accepted and an additional 241 received joint care from both services	Good
Tatlow-Golden et al. [20]	Transitioning from child and adolescent mental health services with attention-deficit/hyperactivity disorder in Ireland: case note review	Republic of Ireland	Retrospective case note analysis	See McNicholas et al. [5]. Sample of YP with ADHD included in this paper	20 YP who crossed CAMHS transition boundary and had a diagnosis of ADHD	None of these YP were directly referred to a public AMHS	Good