Abstract
Background: Sex differences in the frequency and timing of attention-deficit/hyperactivity disorder (ADHD) diagnosis exist. While there are multiple known individual and wider consequences for young females with delayed or undiagnosed ADHD, little is known about mental health service utilisation (HSU) impacts.
Methods: A national population-based cohort of females aged 18-24 years between July 1, 2021, to June 30, 2022, in Aotearoa New Zealand was established. ADHD-index, intellectual disability (ID)-index and age at index were derived using established algorithms. Four mental and two non-mental health variables capturing HSU interactions between July 1, 2022, to June 30, 2024 were derived and analyzed for ADHD-index participants. Unadjusted and adjusted modified Poisson regression models were utilised and reported. All analyses were stratified by ID-index.
Results: Overall, 212,385 females were included, of whom 5244 (2.5%) had ADHD-index. Of those ADHD-indexed, 486 were also ID-indexed. For females ADHD-indexed, 1638 (31.2%) were indexed at age < 12 years, 1575 (30.0%) at age 12-17 years, and 2031 (38.7%) at age 18-24 years. While different patterns emerged between females with and without ID, those with later ADHD diagnosis were associated with higher rates of psychotropic pharmaceutical dispensing, psychiatric inpatient stays, and non-psychiatric hospitalisations compared to those with early diagnosis. For example, in the adjusted analysis comparing females without ID-index who were ADHD-indexed at age 12-17 years to their counterparts indexed at age < 12 years, the estimated incident rate ratio of psychiatric inpatient stay was 2.07 (95% CI 1.20-3.58).
Conclusion: Later ADHD diagnosis among a national cohort of young adult females was common. A later diagnosis was associated with increased mental and non-mental HSU compared to those with earlier diagnosis. Earlier detection of ADHD in females may mitigate their personal burden and reduce subsequent service use.