Psychotic and bipolar disorder diagnoses following contact with child and adolescent mental health services-a longitudinal, nationwide register study of 2 million individuals.

BACKGROUND: Identification of individuals at elevated risk of schizophrenia spectrum and bipolar disorders is a clinical research priority. Current strategies for psychosis risk identification, however, identify only a small proportion of future cases. Additional high-risk approaches are needed, ideally with higher sensitivity, which may include focusing on systems in which risk factors for psychosis are naturally concentrated, such as child and adolescent mental health services (CAMHS). METHODS: We examined the proportion of psychosis and bipolar disorder cases occurring in individuals who had attended CAMHS. The nationwide Danish population born from 1990 to 2020 was followed from 1995 until 2021 using Danish national health registers to retrieve information on contact with CAMHS and diagnoses of the full spectrum of psychotic and bipolar disorders. RESULTS: We followed 1,978,630 individuals for 30,855,257 person-years. Of all diagnoses of psychotic or bipolar disorders in the total population by the end of follow-up, 58.3% occurred among individuals who had attended CAMHS. There was an increased risk of all diagnostic outcomes in CAMHS attendees (HR 15.5; 95% CI 15.5-15.9 for any psychosis or bipolar disorder). The highest risk was in individuals who had an inpatient psychiatric admission in adolescence (HR 46.8, 95% CI 44.8-48.9) where 50% had received a diagnosis of psychosis or bipolar disorder by age 32. CONCLUSIONS: A large proportion of psychotic and bipolar disorder diagnoses in the population occur in individuals who have attended CAMHS. Adolescent CAMHS inpatients are at particularly high risk. These findings highlight CAMHS as a high-capacity, high-risk system for the detection of psychosis and bipolar risk and suggest important potential for large-scale prediction and prevention within CAMHS.