What factors are associated with the age at which autistic adults receive their diagnosis?

Purpose Autism is increasingly being diagnosed in older adults. Undiagnosed autism or a later diagnosis may exacerbate health inequalities experienced. This purpose of this study is to examine factors associated with later age of diagnosis for autistic adults. Design/methodology/approach A retrospective cohort study was carried out, involving adults diagnosed by a National Health Service Autism Assessment Service between July 2022 and June 2023. Routine clinical data was extracted from 234 patient records. Findings High rates of suicidality or self-harm were recorded (n = 139, 59.4%). This was significantly (p < 0.05) associated with a younger age of diagnosis, as was being assessed by Child Adolescent Mental Health Services. Factors associated with a later age of diagnosis were living with a spouse/partner (p < 0.001), having no family support (p < 0.001) and having contact with an adult mental health service (p < 0.01). Under 10% of the sample (n = 23, 9.8%) had attention deficit hyperactivity disorder (ADHD) diagnosed which was much lower than expected from previous evidence detailing co-occurrence with autism. Practical implications Clinicians should be aware of the possibility of undiagnosed autism when adults present with mental health issues, including older adults, even when not considered earlier in life. There are risks for people on autism assessment waiting lists, in particular for suicide and self-harm. Autism diagnostic services should consider the use of risk stratification tools for those on waiting lists. They should consider screening and assessment for other neurodevelopmental conditions like ADHD and record existing diagnoses appropriately. Both primary care services referring to gender clinics and mental health services, should consider screening for autism to support clinical formulation. Originality/value To the best of the authors’ knowledge, this is the first study in the UK to assess factors associated with age of autism diagnosis in adults.