ADHD is reported to be one of the most common psychiatric disorders among children and adolescents, and often persists into adulthood, where its prevalence is 2.8–3.4% (Fayyad et al, 2007; Fayyad et al, 2017). In adulthood, ADHD may be associated with an increased risk of behavioural, psychiatric and somatic comorbid disorders (known as multimorbidity), potentially posing a clinical and economic burden upon public health systems. Healthcare utilisation trajectories from childhood to adulthood among individuals with ADHD remain unclear, and the economic and societal burden of psychiatric and somatic multimorbidity in young adults with ADHD is poorly understood. This prospective, register-based study aimed to assess patterns of healthcare utilisation and expenditure due to multimorbidity during young adulthood in individuals who had been diagnosed with ADHD in childhood. These patterns were also compared between individuals whose ADHD persisted into adulthood, and those who no longer required treatment for their ADHD symptoms.
This study prospectively followed 445,790 young adults (48% female), born between 1987 and 1990 and identified using the Swedish Total Population Register, from the ages of 18 to 26 years. Based on the National Patient Register (NPR), 3534 (0.8%) of these individuals had received an ADHD diagnosis, according to the International Classification of Diseases 10th Revision (ICD-10), before the age of 18 years. ADHD cases were then further categorised, using the NPR and the Swedish Prescribed Drug Register, to identify those who had also received an ADHD diagnosis or were prescribed ADHD medication in adulthood (‘ADHD persisters’; n = 2203 [62%]) and those who no longer sought ADHD-related contact with healthcare services (‘ADHD remitters’; n = 1331 [38%]).
To assess healthcare utilisation and expenditure* due to multimorbidity among the study population, ICD-10 diagnostic codes recorded at inpatient admissions and outpatient visits were coded from the NPR. The associated cost information, according to the primary ICD diagnosis for each individual, was obtained from Sweden’s Cost Per Patient database. ICD diagnoses were categorised into psychiatric (excluding ADHD) and somatic, and the total number of inpatient hospitalisation days, outpatient visits and costs were calculated for psychiatric and somatic disorders per person and by age. Data on utilisation and costs for medication prescription fills were obtained from the Prescribed Drug Register, with medications categorised into psychiatric (excluding ADHD) and somatic, and the total number of prescription fills and costs were calculated for psychiatric and somatic disorders per person and by age.† Generalised estimating equations were used to compare healthcare utilisation (in terms of inpatient visits, outpatient visits and medication prescriptions, and the costs associated with each) between individuals with and without ADHD, and also between the ADHD persister, ADHD remitter and non-ADHD groups, at age 18 years; incremental differences between groups from age 18–26 years were also evaluated.
The authors observed the following differences in healthcare utilisation and expenditure in young adulthood:
ADHD vs non-ADHD at age 18 years
- The mean annual expenditure due to multimorbidity in young adulthood was €890 and €304 for those with and without a childhood ADHD diagnosis, respectively, with annual expenditure consistently greater for the ADHD group than the non-ADHD group across each outcome (inpatient care: €622 vs €165; outpatient care, €152 vs €76; medication prescriptions: €115 vs €63, respectively).
- For psychiatric disorders, healthcare utilisation and expenditure was significantly higher for the ADHD vs non-ADHD group at age 18 years across all outcomes (inpatient days: regression coefficient [B] = 0.20; outpatient visits: B = 0.18; medication prescriptions: B = 0.90) and their associated costs (B = 38.26–155.64).
- For somatic disorders, healthcare utilisation and expenditure was significantly greater for the ADHD vs non-ADHD group at age 18 years across all outcomes and associated costs (inpatient days: B = 0.08; outpatient visits: B = 0.17; medication prescriptions: B = 0.50; inpatient costs: B = 88.40; outpatient costs: B = 37.77) except for medication costs (B = 8.11).
- For both psychiatric and somatic disorders, differences of similar magnitude were observed between the ADHD and non-ADHD groups at age 18 years for inpatient and outpatient visits and costs. However, between-group differences in medication prescriptions and costs were larger for psychiatric than somatic disorders.
ADHD vs non-ADHD throughout young adulthood (18–26 years)
- For psychiatric disorders, differences between the ADHD and non-ADHD groups significantly increased from age 18–26 years for inpatient days (B = 0.06) and medication prescriptions (B = 0.29) and their associated costs (B = 3.32–59.08). However, differences between groups remained stable for psychiatric outpatient visits (B = –0.004) and costs (B = 0.33).
- For somatic disorders, between-group differences significantly increased over time for medication prescriptions (B = 0.05), decreased for outpatient visits (B = –0.01) and costs, and remained stable for inpatient days (B = –0.002). The between-group differences in costs associated with inpatient days and medication prescriptions also remained stable over time.
- For the ADHD group, significantly greater increases vs the non-ADHD group in inpatient care and costs, and the number of medication prescriptions, were observed over time for psychiatric compared with somatic disorders.
Persistent ADHD vs remittent ADHD
- The mean annual expenditure due to multimorbidity was €1060 for ADHD persisters and €609 for ADHD remitters, with greater costs across all outcomes for ADHD persisters (inpatient care: €738 vs €429; outpatient care: €179 vs €110; medication prescriptions: €143 vs €70, respectively).
- Throughout adulthood, ADHD persisters showed significantly greater healthcare utilisation (B = 0.10–2.55) and associated costs (B = 11.80–393.02) across all outcomes compared with individuals who did not have a childhood diagnosis of ADHD.
- On the other hand, ADHD remitters also showed significantly greater healthcare utilisation (B = 0.05–0.50) and associated costs (B = 13.29–243.41) throughout adulthood than the non-ADHD group across all outcomes except for medication costs related to somatic disorders.
- Outpatient visits and number of medication prescriptions, and their associated costs, were significantly greater among ADHD persisters than ADHD remitters, whereas there were no significant differences between the two groups in inpatient days and associated costs.
- Inpatient care was the main driver of costs among young adults who had a childhood ADHD diagnosis, with associated costs being similarly high for both ADHD persisters and remitters. This was primarily attributed to inpatient hospital admissions due to drug abuse (28%), injuries (15%) and autism-spectrum disorders (12%), followed by psychiatric disorders (schizophrenia [7%], depression [7%] and anxiety [5%]).
This study had several limitations, including that the time window for linkage to the Swedish patient registers was limited to 2001–2013, such that a diagnosis of childhood ADHD was based on children receiving an ADHD diagnosis from the age of 10 years, which may have led to an underestimation of the prevalence of childhood ADHD among the study sample. Additionally, the prospective study design may also have led to an underestimation of childhood ADHD cases, since some individuals may not have received a first ADHD diagnosis until adulthood. Furthermore, the authors did not have access to data from wider healthcare services, such as emergency admission or over-the-counter medications, such that cost estimates may have been underestimated.
The authors concluded that childhood ADHD may have long-term associations with psychiatric and somatic disorders in young adulthood, with substantial economic consequences. The higher healthcare utilisation and costs among young adults with a childhood ADHD diagnosis were largely driven by inpatient admissions for drug abuse and injuries, which the authors suggested could represent potential targets for intervention in young adulthood. The authors also emphasised that young adults in remission from childhood ADHD nevertheless showed greater healthcare utilisation and economic burden due to psychiatric and somatic disorders compared with individuals who did not have childhood ADHD. The authors suggested that these results highlight the individual and societal burden of ADHD with multimorbidity in adulthood, and that continued support for individuals with ADHD transitioning from childhood and adolescent to adult health services is important in order to reduce rates of multimorbidity in young adults with ADHD.
*Expenditure was calculated in Swedish crowns (SEK) and inflated to 2017 Swedish prices. The purchasing power parity-based exchange rate in 2017 was €1.00 = 12.165 SEK
†Costs were calculated as days x dose per day x corresponding unit total costs
Du Rietz E, Jangmo A, Kuja-Halkola R, et al. Trajectories of healthcare utilization and costs of psychiatric and somatic multimorbidity in adults with childhood ADHD: a prospective register-based study. J Child Psychol Psychiatry 2020; 61: 959-968.
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