Depression in children and adolescents is a disabling condition that is associated with long-term mental and physical health problems . Screening for depression is one possible solution to improve depression management. In 2005, however, the Canadian Task Force on Preventive Health Care (CTFPHC) determined that there was not sufficient evidence on health outcomes from depression screening to recommend the practice among children and adolescents in primary health care settings . Consistent with this, a 2005 guideline from the United Kingdom’s National Institute for Health and Clinical Excellence (NICE) concluded that universal screening was not advised based on available evidence . In 2009, by contrast, the United States Preventive Services Task Force (USPSTF) concluded that adolescents, but not younger children, should be routinely screened for depression in primary health care settings ‘when systems are in place to ensure accurate diagnosis, psychotherapy (cognitive-behavioral or interpersonal), and follow-up’ (page 1223) . This recommendation was made based on a systematic review of the literature through May 2006 even though, as the USPSTF recognized, there was little data on the accuracy of screening tools and no data to compare health outcomes between screened and unscreened adolescents . In the more than 5 years since that review, a substantial amount of research relevant to depression screening in children and adolescence has been published.
Screening is potentially costly in health care resources and has the potential to cause harm to some children and adolescents who may be diagnosed or treated inappropriately. An important empirical question is whether screening, given these concerns, would be more effective than alternative care models that do not rely on universal screening. As described in a recent critique of calls for depression screening, there are a number of reasons why simply assuming that depression screening would result in more benefit than harm may not be reasonable, including high false positive rates if screening tools are not sufficiently precise, generally small depression treatment effects, and the inconsistent quality of routine care that is often provided [5
]. Thus, the objective of the proposed systematic review is to evaluate the mental health effects of screening children and adolescents aged 6 to 18 years for major depressive disorder (MDD) in medical or community settings. To do this, we identified the following key questions based on well-established criteria delineated by the World Health Organization [6
] and the United Kingdom National Screening Committee [7
], as well as the methodological framework of the USPSTF for evaluating screening programs [8
: What is the accuracy of depression screening instruments to detect cases of MDD among (a) children and (b) adolescents?
: Is treatment of MDD during (a) childhood and (b) adolescence effective in improving symptoms of depression?
: Is depression screening during (a) childhood and (b) adolescence more effective than usual care in (i) improving depressive symptoms or (ii) reducing the number of MDD diagnoses?
: What are the potential harms associated with depression screening, including treatment, during (a) childhood and (b) adolescence?
Major depressive disorder in children and adolescents
Depression is primarily characterized by the core symptoms of persistent sad mood or irritability and/or a loss of interest or pleasure in activities that are normally enjoyed. Among children and adolescents, irritability may be more prominent than sad mood, and tantrums and other disruptive behavior may also be important markers. In North America, MDD is diagnosed among children and adolescents based on criteria established by the American Psychiatric Association and delineated in the 4th Edition of the Diagnostic and Statistical Manual (DSM-IV) . Criteria for a diagnosis of MDD include having at least five of nine depressive symptoms for 2 weeks or more, at least one of which must be depressed mood, including irritability, or loss of interest in activities. Symptoms must cause significant distress or impairment in daily function. MDD should be distinguished from bipolar disorder, which is characterized by abnormal and disruptive elevated moods, in addition to depression. The DSM-IV also includes dysthymic disorder, which is a longer lasting, but less severe, mood manifestation than MDD, as well as minor depressive disorder, which requires only two, rather than five, depressive symptoms. This review, consistent with earlier reviews by the CTFPHC  and the USPSTF  will assess evidence relevant to screening for MDD, but not dysthymic disorder or minor depression, for which treatment options and efficacy are much less well delineated. It will also include studies relevant to screening for depression based on the International Classification of Diseases (ICD) definition of depression, which is similar to the DSM-IV definition .
Prevalence and burden of depression in children and adolescents
A 2006 meta-analysis that synthesized data from over 60,000 adolescents aged 13 to 18 years estimated the point prevalence of MDD to be 5.6% in the community with rates slightly higher among girls than boys . In Canada, a study of almost 18,000 respondents to the National Population Health Survey (1995 to 1996) found that 4.8% of boys and 8.7% of girls had an episode of MDD in the past year. Among youth aged 12 to 14 years, the rates were 2.7% for boys and 2.6% for girls. For adolescents aged 15 to 19 years, 6.1% of boys and 12.5% of girls had experienced at least one episode . Compared to community samples, in medical settings the rate may be up to twice as high . Some research has suggested that the lifetime prevalence of an episode of MDD among adolescents may be as high as 20% [1, 14, 15]. In Canada, however, a study that used data from the Canadian Community Health Survey Cycle 1.2 reported a lifetime prevalence rate among almost 3,000 adolescents aged 15 to 19 years of 7.6% for MDD, including 4.3% for males and 11.1% for females . Among youth under age 13, the point prevalence of MDD has been estimated to be approximately 3% .
MDD in childhood and adolescence is associated with many negative outcomes, including behavioral problems and poor school performance, early pregnancy, and impaired social, work, and family functioning in adolescence and into adulthood . Many studies have shown that patients with depression in adulthood had at least one episode of MDD in childhood or adolescence, and there is a high rate of recurrence among youth with MDD [1, 15, 17–19]. Despite this substantial burden, relatively few children and adolescents with depression receive treatment [20–22].
What is depression screening and when should it be recommended?
Screening is a preventive strategy that is traditionally used to detect disease in patients who otherwise have no signs or symptoms. Screening programs are premised on the assumption that early detection of disease will enable earlier and more effective intervention. Unlike screening for most other medical diseases, however, screening for depression does not seek to achieve early identification of pre-symptomatic cases that will subsequently evolve into psychiatric disorder. Rather, screening for depression involves the use of depression symptom questionnaires or small sets of questions about depression to identify patients who may have current depression, but who have not sought treatment and whose depression has not already been recognized by health care providers. Patients identified as possible cases need to be further assessed and, if appropriate, offered treatment. Depression screening is potentially useful only to the extent that it improves patient outcomes beyond any treatment that is provided as part of standard care. Thus, to be successful, a screening program must identify a significant number of depressed patients who are not already diagnosed with depression, engage those patients in treatment, and obtain sufficiently positive treatment results to justify costs and potential harms from screening .
In 1968, the World Health Organization issued a report that delineated criteria to determine whether conditions are suitable for screening , and the main elements of those criteria continue to be used today . Generally, it is reasonable to consider screening when the condition in question is important and prevalent, can be effectively treated, and cannot be readily detected without screening. Further, screening methods should be accurate and carry only a tolerably small risk of false positive results, which could lead to unnecessary diagnostic testing, adverse effects, costs of inappropriate treatment, and to sequelae of being incorrectly labeled, such as stigma. False reassurance for false negatives may also need to be considered in some circumstances. The principal criterion is that there must be evidence that benefits from screening outweigh potential harms. Ideally, benefits in excess of potential harms should be demonstrated consistently in well-conducted randomized controlled trials (RCTs) with sufficiently long follow-up to cover the time horizon of important patient-oriented outcomes.
Current practices in depression screening in childhood and adolescence
Studies from community  and health maintenance organization  settings in the United States published in 2000 and 2001 suggested that 40% to 60% of adolescent patients may be screened for depression based on physician report, but this number fell to only 3% when medical charts were examined for documentation of screening . More recently, TeenScreen, an American organization based at Columbia University, has aggressively promoted widespread mental health screening for adolescents and has reported that they received more than 400,000 requests for screening questionnaires from schools, primary-care physicians and managed-care organizations in 2010 alone . There are numerous reports of mental health screening supported by TeenScreen being conducted routinely in medical practices and across entire school districts in the United States [27–29]. In Canada, the governments of Alberta and Manitoba, for instance, have called for widespread depression screening in school settings as part of long-term plans to improve youth mental health [30, 31].
Existing guidelines and recommendations
In Canada, the last guideline statement on the topic was a CTFPHC recommendation from 2005 . The CTFPHC recommendation focused on adult depression, but noted that, consistent with previous findings from the USPSTF, there was not enough evidence to support a recommendation for screening in child or adolescent medical care settings. Similarly, a 2005 NICE guideline on depression management for children and youth in the United Kingdom emphasized the importance of better and more consistent care, but concluded that the evidence needed to support a screening recommendation was not available . More recently, in 2009, the USPSTF issued a recommendation that adolescents in medical settings should be screened for depression in primary-care settings when integrated care systems are in place to ensure accurate diagnosis, competent psychotherapeutic and medical support, and follow-up . The recommendation document focused on the prevalence and burden of depression among adolescents, as well as the existence of screening tools and treatments, but not on evidence from any RCT that mental health outcomes improved among youth who were screened compared with youth who were not screened for depression . Calls for depression screening have gone beyond medical settings. The 2003 United States President’s New Freedom Commission on Mental Health called for screening in primary medical care, school, and child welfare settings as the key to reducing the community burden of depression , and school-based screening programs have been implemented in Canada . Existing guidelines and recommendations, however, have not directly addressed whether school-based screening outside of the context of health care settings is recommended.
Previous systematic reviews and meta-analyses
A number of reviews have assessed the accuracy of screening tools for detecting MDD, the efficacy of treatments, and harms that may be associated with depression treatment in children or adolescents (see Additional file 1). Only one review , a United States Agency for Healthcare Research and Quality (AHRQ) report, which was done in conjunction with a USPSTF guideline , has assessed the various components of a depression screening program for children or adolescents (accurate screening tools, effects of treatment, effects of screening, potential harms) and whether there was evidence that mental health outcomes were better for screened versus non-screened children and adolescents. The review was published in 2009, but only included studies through a search that was done through May 2006. The review included nine studies on the accuracy of six different depression screening tools, but reported that all had serious methodological flaws, including non-random patient selection, excessive delays between administration of screening tools and diagnostic interviews, high levels of attrition, poor reporting of methods and results, and small samples. No studies were rated as being of good quality. The review identified 18 fair- to good-quality RCTs on treatment for MDD with psychotherapy, medication, or a combination of psychotherapy and medication, and concluded that treatments were generally effective, but that not all medications appeared to work well. There were no studies identified that examined mental health outcomes among children or adolescents who were screened compared to children and adolescents who were not screened.