Autism spectrum disorder (ASD) is a neurodevelopmental disorder with highly variable presentation, developmental trajectories and outcomes. While traditionally considered a lifelong condition, recent evidence suggests that the diagnostic status may evolve over time in certain individuals. The aim of this systematic review with meta-analysis is to investigate long-term stability of ASD diagnosis at different developmental periods, considering the impact of diagnostic instruments, duration of follow-up and characteristics of individuals.
A systematic search following PRISMA 2020 guidelines using MEDLINE, PsycINFO and CINAHL. Studies included were longitudinal in design, published from 2014, with a follow-up period of 24 months or longer and had defined diagnostic criteria applied at both baseline and follow-up. Nine eligible studies (n = 4,436) were identified, and the pooled estimates of diagnostic stability were derived from the fixed- and random-effects models. Subgroup analyses assessed differences by follow-up, approach to diagnosis and age at diagnosis to age at follow-up.
Diagnostic stability estimates varied widely, with a pooled proportion of 84.6% using a random-effects model, reflecting substantial heterogeneity (I² = 98.79%). Higher stability was observed in long-term follow-up (>10 years, 88.2%) and in cases diagnosed in early childhood when followed up to adolescence. Use of combined diagnostic tools (ADOS, ADI-R) with clinical judgement yielded higher stability (90.6%) than clinical judgement alone (67.6%). Cognitive ability, early language and co-occurring conditions were key moderators of diagnostic change. Diagnostic loss did not always equate to functional recovery, raising concerns about access to support.
Although many individuals retain their ASD diagnosis over time, diagnostic reclassification is not uncommon, especially among high-functioning individuals and those diagnosed later in life. Findings support a developmental, needs-based assessment and care. The study highlights the need for standardised diagnostic practices, as well as global inclusive longitudinal research to guide policy and equitable service provision.
