Age at diagnosis and diagnostic delay across attention-deficit hyperactivity and autism spectrums

Background: Despite the known benefits of accurate and timely diagnosis for children with attention-deficit hyperactivity disorder and autism spectrum disorders (autism), for some children this goal is not always achieved. Existing research has explored diagnostic delay for autism and attention-deficit hyperactivity disorder only, and when attention-deficit hyperactivity disorder and autism co-occur, autism has been the focus. No study has directly compared age at diagnosis and diagnostic delay for males and females across attention-deficit hyperactivity disorder, autism and specifically, attention-deficit hyperactivity disorder + autism. Methods: Australian caregivers (N = 677) of children with attention-deficit hyperactivity disorder, autism or attention-deficit hyperactivity disorder + autism were recruited via social media (n = 594) and the Monash Autism and ADHD Genetics and Neurodevelopment Project (n = 83). Caregivers reported on their child’s diagnostic process. Diagnostic delay was the mean difference between general initial developmental concerns and the child’s attention-deficit hyperactivity disorder and autism diagnosis. Results: Children with autism were significantly younger at autism diagnosis than the attention-deficit hyperactivity disorder + autism group (η_p² = 0.06), whereas children with attention-deficit hyperactivity disorder were significantly older at attention-deficit hyperactivity disorder diagnosis than the attention-deficit hyperactivity disorder + autism group (η_p² = 0.01). Delay to attention-deficit hyperactivity disorder and autism diagnosis was significantly longer in the attention-deficit hyperactivity disorder + autism group compared to attention-deficit hyperactivity disorder (η_p² = 0.02) and autism (η² = 0.04) only. Delay to autism diagnosis for females with autism (η² = 0.06) and attention-deficit hyperactivity disorder + autism (η² = 0.04) was longer compared to males. Conclusions: Having attention-deficit hyperactivity disorder + autism and being female were associated with longer delays to diagnosis. The reasons for these delays and possible adverse effects on outcomes require further study.