After duplicates were removed, 18,287 studies remained for screening by title and abstract. 213 studies were included for full-text screening, of which 200 studies were excluded to leave 13 studies for inclusion in this review, representing 10 different cohorts of young people crossing the CAMHS transition boundary. Figure 1 illustrates the paper selection process. Only one study explored mental health outcomes after transition ; however, this data could not be extracted as CAMHS leavers were grouped with looked after children. Therefore, only information on service use outcomes following transition will be discussed in this review.
The 13 included studies represent research carried out in six different countries, Canada , England [2,3,4, 16, 18, 19], the Republic of Ireland [5, 20], France , Australia , and Italy [23, 24]. Two studies were service evaluations [17, 19]: one was a questionnaire study , one was a longitudinal study , and the remaining nine had a retrospective cohort study design [2,3,4,5, 18, 20,21,22,23]. Seven of the studies involved all young people in a cohort of CAMHS leavers, whilst four focused only on young people with attention-deficit/hyperactivity disorder (ADHD) [2, 19, 20, 24]. The sample sizes in the included studies ranged from 20 to 4226 young people. Table 2 shows further details of the included studies.
Risk of bias
The quality of the included studies varied, with 10 being of good quality and three being of poor quality (see Table 2 for more details). Studies were rated as poor if they did not include a measure of clinical need to transition or a breakdown of transition for different subgroups (e.g., different diagnoses, age groups, severity of illness, etc.) and if detailed baseline information of the cohort was missing.
Synthesis of results
The synthesis of individual study findings shows a care gap at the end of CAMHS, with only 24% of young people transitioning to AMHS after reaching their CAMHS age boundary (see Table 3 for details). Three studies [4, 5, 16] explored the service use destinations of young people who had an ongoing clinical need at the end of CAMHS and found that some did not receive an AMHS referral, despite still being judged to need ongoing care, with figures ranging from 42 to 84% (the latter figure includes some looked after children in Memarzia et al. ). In addition, four studies [19, 20, 22, 24] showed that 103 young people were discharged from CAMHS, only for them to be referred to AMHS by their GP.
A quarter of young people remained at CAMHS after crossing the transition boundary, whilst another quarter transitioned to AMHS. The other 50% had varied service use destinations; however, in most studies, the follow-up periods were not long enough to find out what happened to these young people after being discharged from CAMHS. Disengagement was high, with all but four studies [16, 22,23,24] including disengagement as an outcome after young people left care at CAMHS. The number of young people who were discharged due to disengagement was recorded in all but one study , with disengagement ranging from 3 to 40% of young people.
Two studies [3, 5] reported young people not being referred to AMHS, because CAMHS clinicians did not think that young people would meet the inclusion criteria or that AMHS did not have the necessary expertise. Five studies recorded unsuccessful referrals to AMHS [5, 18, 21,22,23], with percentages of referrals rejected ranging from 3 to 73%. Full details of young people’s service use outcomes following reaching the upper age limit of their CAMHS service is shown in Table 3.
Three studies evaluated how many young people experienced optimal transition, two [4, 21] according to the four principles of ‘optimal transition’ identified by Paul et al. . In most cases, optimal transition was not achieved, with percentages of young people having optimal transition recorded at 6% , 13% , and 4% .
Three studies explored the average waiting times which young people experienced during their transition to AMHS [5, 17, 21]. All found that young people experienced long delays, ranging from 55 to 110 days.
Three studies looked at engagement at AMHS following transition, the TRACK study (as reported by [3, 4]), Ogundele , and Schandrin et al. . Of the 134 young people in these studies who transitioned to AMHS, 115 (86%) had at least one appointment. Rates of engagement fell further after this first appointment, with 16% being discharged after one AMHS appointment in the TRACK study  and 55% being discharged in the 1–3 years following transition in the study by Schandrin et al. .
Outcomes of young people with ADHD
Four studies focused on young people with ADHD. One was a service evaluation following improvements to their transition process , and this showed a much higher rate of transition to AMHS (38%) than the other three studies carried out in the standard care (11%). In two of the studies involving young people with ADHD, none of the cohort was transitioned to an AMHS at the CAMHS age boundary [20, 24]. Of the young people who were discharged to their GP following cessation of care in CAMHS, one-third were then referred to an AMHS, implying that they were discharged despite having an ongoing clinical need for treatment.