Background
Remarkable advances in pediatric healthcare over the past century have substantially reduced overall childhood morbidity and mortality, while concomitantly enabling some children with complex chronic conditions (CCC) to survive and live longer. A clear definition of these CCCs is important for several reasons: to assess population-level temporal trends in the proportion of morbidity and mortality associated with CCCs; to assess patterns of healthcare utilization among patients with CCCs; and to perform individual-level risk adjustments for patients’ CCC status in studies of healthcare processes and outcomes.
In 2000, Feudtner and colleagues developed a definition for CCCs: “Any medical condition that can be reasonably expected to last at least 12 months (unless death intervenes) and to involve either several different organ systems or 1 organ system severely enough to require specialty pediatric care and probably some period of hospitalization in a tertiary care center”[
1]. Based on this definition, a comprehensive set of codes available at that time from the International Classification of Disease version 9 Clinical Modification (ICD-9-CM) system were identified as indicative of a CCC, and further categorized into 9 categories (cardiovascular, respiratory, neuromuscular, renal, gastrointestinal, hematologic or immunologic, metabolic, other congenital or genetic, and malignancy).
The CCC classification system (v1) can be used to either examine a particular CCC category or to identify patients with multiple CCC categories. The CCC system was initially applied to studying patterns of pediatric mortality and end-of-life care [
1,
2], and has subsequently been applied to a variety of research problems, including risk adjustment, prediction of adverse health outcomes, and identification of populations with high health care utilization [
3‐
27].
The original CCC system, now more than a decade old, warranted revision for 3 main reasons. First, the International Classification of Disease 10th Revision (ICD-10) is replacing the ICD-9 system in the United States. Although already widely used internationally, ICD-10 was first used in the Centers for Disease Control and Prevention vital statistics data files in 1999, and government diagnostic and procedural billing codes will change to ICD-10 in 2015. Second, the original CCC system has not been updated to include new diagnostic codes added over the past decade, and in particular the original CCC system does not include a category for conditions originating in the neonatal period. Third, the original CCC system consisted entirely of diagnostic codes and lacked a domain of codes that specify either a likely dependence upon medical technology or having undergone organ (including bone marrow) transplantation, both of which would indicate CCC status.
In this study, we report on our updated CCC version 2 (v2) classification system, which we implemented for both the ICD-9 and ICD-10 coding schemes. We evaluated the CCC v2 system in three ways: 1) the comparability between the ICD-9 and ICD-10 systems; 2) the year-to-year stability of classification across CCC v2 attributable to cause of death in 1991–2010; and 3) the proportions of patients classified as having a CCC between CCC v2 and CCC v1 systems.
Discussion
Children with complex chronic conditions present challenges and opportunities in delivering healthcare, which necessitates classification schemes that can distinguish children across a spectrum of pediatric health states [
31,
32]. This spectrum of health states comprises several related but distinct dimensions: the degree of functional capacity or impairment across several domains of function; the hazard that a disease or condition poses to function or life; and the ease or difficulty of curing or ameliorating the disease. These dimensions are bundled into the notion of
health state and the related concept of a
health (or illness) trajectory (a phrase that we are using to connote the likely pattern of change of health over time).
The multidimensional nature of both health states and health trajectories reinforces that no single uniform classification system is likely to serve all the different goals of research or quality improvement projects that study the needs of children with complex chronic conditions. Instead, an ideal system should be flexible and capable of being adapted to address each particular research question. The system should also be transparent regarding how it is constructed, implemented, and subsequently audited, which can be facilitated by providing open source code that can be reviewed and modified by end-users. Finally, the system should be multidimensional, meaning that the system should capture different components of health states and health trajectories.
The original CCC v1 system aimed to identify infants, children, and adolescents diagnosed with complex chronic conditions, with an emphasis on examining patterns of mortality and of end-of-life healthcare utilization associated with CCCs. The system was built around ICD-9 codes, which were grouped into categories of disease to track different anatomical and physiologic pathologies associated with the different health states and trajectories.
The CCC system is flexible in that this classification system can be used to examine a particular CCC category or to identify patients with multiple CCC categories and significant multisystem comorbidities. Patients with >1 CCC category have a higher risk of increased inpatient readmission rate and ultimately death [
22,
33,
34]. Furthermore, pediatric patients with multiple CCC categories are increasingly prevalent in US hospitals [
35]. For datasets where individuals can be tracked over multiple encounters, the CCC system also can be used to classify patients based on their cumulative CCC status aggregated over time.
The updated CCC v2 is more comprehensive than the original CCC system, having incorporated additional new CCC diagnoses, a category of neonatal CCCs, and domains for technology dependent or post-transplant related conditions. The addition of the neonatal category caused several CCC diagnoses to shift to this new category (for example, chronic respiratory disease arising in the perinatal period [ICD-9: 770.7] had been classified as a “respiratory” CCC in CCC v1, but now is classified as a “neonatal” CCC in CCC v2). In future studies with CCC v2, however, investigators should keep in mind that the increased sensitivity in identifying children with complex chronic conditions may have decreased specificity.
The domain of technology-dependent and post-transplant related condition captures conditions that are increasingly prevalent with advances in medical technology and treatments [
29]. A single institution study reported that 41% of patients discharged from a children’s hospital in 2000 were dependent upon medical technology (20% upon medical devices, 32% upon medicines, and 11% upon both devices and medicines) [
28]. A national study revealed that in 2006, patients with CCCs accounted for 73% of gastrostomy tube placements, 75% of tracheostomy tube placements, and 92% of cerebrospinal fluid shunts [
22]. By identifying this population of CCC patients, we will be able to better evaluate the experiences of technology-dependent and transplanted children, examine their patterns of health care utilization, and design programs to provide coordinated, efficient, and cost-effective care.
Importantly, the CCC v2 system can be implemented for either the ICD-9 or the ICD-10 coding scheme. With the mandated transition from ICD-9 to ICD-10 coding schemes for medical diagnoses and procedures, the CCC v2 system provides a necessary update. We tested the comparability of CCC v2 between ICD-9 and ICD-10, and found no significant discrepancies in CCC categories between the ICD-9 and ICD-10 schemes. We also examined the temporal trends of CCC categories attributable to cause of death during 1991–2010, and did not find any drastic changes at the 1999 time point, when ICD-10 coding was implemented, and no discontinuities in long-term time trends.
We did observe minor declines in the cardiovascular and respiratory CCC categories in the CDC Multiple Cause of Death 1991–2010, which corresponded with a reduction in overall population death rates in heart disease and chronic lower respiratory diseases [
36], which have been attributed in part to reductions in tobacco use [
37,
38], but for pediatric patients, are more likely due to improved cardiac and pulmonary care. The minor increases in the congenital/genetic CCC were most likely related to improved diagnostic capabilities, such as the improved detection of genetic diseases through advancements in newborn screening processes. Nevertheless, none of these trends demonstrated substantial shifts over the 20-year period. This suggests that CCC v2 has close comparability between ICD-9 and ICD-10, and that the transition from ICD-9 to ICD-10 is unlikely to substantially change CCC v2 proportions, or cause a significant discontinuity in time trends.
We also measured the degree to which the CCC v2 system identified more patients with complex chronic conditions than CCC v1 because of the modifications and additions. While most CCC categories demonstrated moderate or almost no change (such as the congenital/genetic CCC) in the percentage of all deaths attributed to a given CCC category, there were several CCC categories had notable increases in percentages when the CCC v2 system was applied (such as the gastrointestinal CCC); and the change in the percentage of cases assigned to a CCC category also varied when the schemes were applied to different national data sources (for example, the percentage of patients with gastrointestinal CCC increased 226% in the KID but increased 333% in the NEDS). Cardiovascular CCC and malignancy CCC both decreased in NEDS and KID. These decreases were due to the elimination of self-limiting or completely correctable cardiovascular conditions (ICD-9: 745.4, 745.5, 747.0, and 745.7) and benign neoplasms (ICD-9: 210–229) in the CCC v2 scheme.
Acknowledgements
Funding/Support
This study was supported in part by the Agency for Healthcare Quality and Research, Comparative Effectiveness and Safety of Hospital-Based Pediatric Palliative Care (1R01HS018425).
Role of the sponsor
The funding organization had no role in the conduct of the study, including the collection, analysis, and preparation of the data or the drafting, editing, review, or approval of the manuscript. The content is solely the responsibility of the authors and does not necessarily represent the official views of the Agency for Healthcare Research and Quality.
Competing interests
The authors declare that they have no relevant financial relationships and no relevant non-financial relationships to disclose.
Authors’ contributions
All authors contributed to the conception and design of the study, implemented different aspects of the analysis, drafted sections of the manuscript, revised the manuscript, and approved the final version for submission.