Factors associated with age at autism diagnosis in a community sample of Australian adults.

Autism diagnosis in adulthood has become increasingly common due to a range of factors including changes in awareness, diagnostic criteria, and professional practices. Past research identified a range of demographic and autism-related factors associated with autism diagnosis age in children. However, it is unclear whether these apply to autistic adults. This study aimed to examine predictors of autism diagnosis age in adults while controlling for current age and autistic traits. We used a cross-sectional sample of 657 adults aged 15-80 from three self and carer-report studies: the Australian Longitudinal Study of Autism in Adulthood (ALSAA), Study of Australian School-Leavers with Autism (SASLA) and Pathways, Predictors and Impact of Receiving an Autism Spectrum Diagnosis in Adulthood (Pathways). Using hierarchical multiplicative heteroscedastic regression, we found that older current age and higher self-reported autistic traits predicted older diagnosis age, and that female gender, lack of intellectual disability, language other than English, family history of autism, lifetime depression, and no obsessive-compulsive disorder predicted older diagnosis age beyond current age and autistic traits. The paradoxical relationship between high autistic traits and older diagnosis age requires further investigation. Based on these findings, we recommended strategies to improve autism recognition in women and people from non-English-speaking backgrounds. Future studies could extend the findings by examining the effects of childhood and adulthood socioeconomic status on adult diagnosis age. LAY SUMMARY: We studied the relationship between age at autism diagnosis and other characteristics in adults. We found that both older current age and higher autistic traits, female gender, language other than English, family history of autism, and history of depression were related to older age at diagnosis, while intellectual disability and history of obsessive-compulsive disorder were related to younger age at diagnosis. Our findings suggest more work is needed to help recognize autism in women and people from non-English-speaking backgrounds.