Childhood-onset complex chronic conditions (4Cs) are long-standing medical conditions that begin in childhood. It affects multiple organ systems and requires specialized and coordinated care. Although individuals with 4Cs represent a relatively small proportion of the pediatric population, they account for a disproportionate share of inpatient healthcare utilization and costs. Advances in pediatric medicine have substantially improved survival, resulting in a growing population of individuals with 4Cs reaching adulthood. Existing studies of adults with pediatric onset conditions have been limited by narrow disease definitions, lack of appropriate comparator groups, exclusion of major conditions like cystic fibrosis and sickle cell disease, and limited generalizability. Consequently, there remains a critical gap in understanding the system-level impact of 4Cs in adult inpatient care settings.
A study published in the JAMA Network aimed to detect, characterize, and evaluate acute care hospitalizations in young adults with childhood-onset complex chronic conditions in a universal healthcare system. The study sought to quantify the prevalence of 4Cs in young adult hospitalizations and to compare hospital outcomes between young adults with and without 4Cs. The primary hypothesis was that young adults with 4Cs would experience higher hospital resource use, specifically longer lengths of stay, than their peers without 4Cs.
This retrospective cohort study used data from the General Medicine Inpatient Initiative (GEMINI) research network, which contains detailed clinical and administrative data from adult medical and intensive care unit admissions at 29 hospitals in Ontario, Canada. The analysis was restricted to hospitalization occurring from January 1 to December 31, 2018, to avoid confounding related to the COVID-19 pandemic. The cohort included patients aged 18 to 39 years, capturing the post-transition period while maintaining specificity for conditions originating in childhood.
Childhood-onset complex chronic conditions were detected using an adapted version of the widely used pediatric complex chronic condition (CCC) ICD-10 algorithm. Clinicians categorized CCC codes as “most likely pediatric,” “possibly pediatric,” or “not pediatric” because adult hospital data lack information on age at diagnosis. The primary analysis conservatively defined 4Cs using only “most likely pediatric” codes, with sensitivity analyses applying broader definitions. Analyses were conducted at the level of each patient’s first hospitalization to reduce bias from repeated admissions. Propensity score-based overlap weighting was used to balance baseline characteristics between groups. Primary outcomes included length of stay, in-hospital mortality, and ICU admission. Secondary outcomes included total inpatient cost, number of medications, advanced imaging use, and 30-day readmission rates.
Among 19,915 hospitalizations involving 15,072 unique young adults, 1,329 hospitalizations (6.7%) involved at least one 4C, representing 814 patients (5.4%). Most patients with 4Cs had only one such condition (92.7%). The most common 4Cs were hereditary anemias (26.0%), cystic fibrosis (17.0%), cerebral palsy (11.8%), brain and spinal cord malformations (7.2%), and congenital heart and vessel malformations (7.0%). Patients with 4Cs were younger and had lower Charlson Comorbidity Index (CCI) scores, were more frequently admitted to teaching hospitals, and had higher illness severity scores (median modified Laboratory-Based Acute Physiology Score 15.0 vs 10.0) at weighting.
Hospitalizations involving 4Cs accounted for 10.7% of all adult hospital bed-days despite representing a small proportion of admissions. After overlap weighting, index hospitalizations with 4Cs were linked to significantly longer lengths of stay (relative ratio [RR]: 1.62, 95% confidence interval [CI]: 1.48 to 1.77) and higher total hospital costs (RR: 1.65, 95% CI: 1.05 to 2.59). Patients with 4Cs received more medications (RR: 1.26, 95% CI: 1.19 to 1.34) and had higher 30-day readmission rates (RR: 1.59, 95% CI: 1.28 to 1.98). There were no statistically significant differences observed in in-hospital mortality (RR: 1.43, 95% CI: 0.87 to 2.33) or ICU admission rates (RR: 1.05, 95% CI: 0.91 to 1.20). Sensitivity analyses by using broader 4C definitions and restricting the cohort to ages 18 to 24 years produced similar results.
Young adults with 4Cs represent a small but highly resource-intensive population in adult inpatient care. These individuals experience longer hospital stays, higher costs, and more frequent readmissions than their peers without 4Cs, despite lower traditional comorbidity scores. The findings suggest that commonly used adult comorbidity indices inadequately capture complexity in the younger adults and that adult health systems could benefit from care models adapted from pediatric complex care. Targeted inpatient and outpatient interventions for this growing population may reduce hospital utilization, improve care transitions, and enhance health system efficiency.
References: Malecki SL, Shen T, Loffler A, et al. Characteristics and Outcomes of Adults Hospitalized with Childhood-Onset Complex Chronic Conditions. JAMA Netw Open. 2026;9(1):e2553610. doi:10.1001/jamanetworkopen.2025.53610
