Increasing recognition of the health, economic, and social adversity endured by children with medical complexity (CMC) and their families commands substantial clinical, research, and policy attention.1 ,2  Major initiatives wrestle with the practical challenge of identifying the relevant CMC population. Because many ways to identify CMC exist, different populations are created when different identification tools are applied.2  A standard definition is naturally attractive for those committed to advancing CMC health because when inconsistent definitions are used across initiatives, combining or comparing results may be impossible. For example, if 1 health system uses an International Classification of Diseases–based system to identify eligible CMC for its care coordination program and another uses a combination of clinical and social characteristics from electronic health records and family surveys for its program, outcome differences between programs might exist not because one is more effective but because differences in defining populations lead to varied responses. Standard definitions could also help youth, families, and advocates coalesce their efforts around a common identity.

In this issue of Pediatrics, Millar et al’s thought-provoking article3  explores how clinicians and researchers with expertise in medical complexity view specific criteria to operationalize Cohen et al’s 4-domain medical complexity definitional framework.4  This definitional framework identifies CMC as the children at the intersection of having complex chronic health problems, severe functional limitations, substantial service needs, and high health care use. This is arguably the field’s most widely accepted conceptualization of CMC. Following a scoping literature review, Millar et al drafted a set of detailed criteria to reflect each domain, such as, “The child experienced an ICU readmission within 30 days of a previous ICU admission” for the health care use domain. Eighty-one experts participated in a Delphi process which reduced 55 candidate criteria into a final set of 39. Notably, the health care use and family needs domains included 13 and 23 criteria, respectively. The authors integrated social drivers of health throughout the family needs domain.

This study marks an important additional step on a lengthy road toward an operationalizable standard definition of CMC. Millar et al recognize that even with a rigorous Delphi process, eliminating subjectivity from the criteria as well as heterogeneity in the resulting CMC population is challenging. Because youth and families of CMC were not part of the Delphi panel of experts, the authors acknowledge the needed plan to integrate their input in the future. This raises an important question: “How does having a standard definition of CMC (and therefore of non-CMC as well) help children and families?” As authors of this commentary, we offer the shared perspective of a parent of a child with medical complexity who frequently collaborates on health system projects (D.M.G.) and a pediatrician and researcher working with CMC (R.J.C.). In fact, less is known about how standard definitions assist CMC and families, and the work by Millar et al inspires several important considerations.

In 2015, a group of authors wrote a practical summary of common techniques to identify CMC5  rooted in the 2011 Cohen et al definitional framework.4  Beyond “how” to identify CMC, the authors foreshadowed an incisive question of “why” identify CMC. The vast array of underlying conditions leading to medical complexity, many of which are rare, makes a universal standard a daunting endeavor. Reasons for selecting a specific technique to identify CMC often serve a specific purpose such as clinical or service program eligibility, policy analysis, or research. Flexibility in choosing a technique can help individuals match identification tools to available data structures, overall objectives, and existing resources; and standard definitions not calibrated to purpose can face competing dilemmas. For example, if program eligibility criteria and capacity are mismatched, the number of CMC seeking enrollment may overwhelm program providers and degrade services. Additionally, the dynamic nature of CMC comorbidities may lead to contradictory scenarios where a child’s eligibility can turn on or off over short timeframes. The stakes can be high if meeting the medical complexity definition is tied to eligibility for resources. With any definition, avoiding barriers that require families to perpetually justify eligibility is important.

In the Advancing Care for Exceptional Kids Act, the 2019 federal legislation to enhance care coordination for children with complex medical conditions within Medicaid, medical complexity was defined as either (1) ≥1 chronic condition affecting three or more body systems that severely reduces cognitive or physical functioning and requires medication, durable medical equipment, therapy, etc., or (2) 1 life-limiting illness or rare pediatric disease as defined in the Federal Food, Drug, and Cosmetic Act. However, the Secretary of Health and Human Services retained discretion to change these criteria, effectively altering what is defined as medically complex in this context. The flexibility is likely intended to calibrate services to resource availability; and as clinical services evolve over time,6  the threshold for what is considered complex care might increase.

Another set of considerations relates to whether a standard definition of CMC should reflect intrinsic personal and biological characteristics or the nature of the system and social environment in which a child lives. Although health system function and social context affect child health, it can be less clear where these fit in a CMC definition. For example, should inadequate care coordination define medical complexity or define the malfunctioning system in which medical complexity exists? In Millar et al’s consensus criteria, unmet needs are represented in several criteria (eg, “the child is experiencing complications resulting from unmet care needs”) likely because they are a recognized serious problem.7  In highly functional or idealized systems of care, unmet needs are minimized. If meeting family needs from the child’s conditions requires a system to perform complex work, the child might still be considered to have medical complexity even if those needs are met. The presence of needs—whether met or not—may be the more important concept for defining medical complexity.

When CMC definitions include system function, social context, and outcomes of medical complexity, avoiding inconsistencies in the attribution of medical complexity to a child may be important. Presumably, when medical complexity exists in 1 context (eg, inadequate respite), it should still exist in another for the same child (eg, if moving to a new environment improved respite access). Family reporting of needs being met can be highly variable,7  which poses a risk for inconsistency. Because underreporting can be driven by mistrust, discrimination, and other experiences,8 ,9  attention is needed to avoid exacerbating inequities if certain groups are less likely to report issues that are used to define complexity.

Existing tools have different sensitivity and specificity for identifying a CMC population when compared with expert chart review, and for predicting CMC outcomes.5 ,10 ,11  They also have different degrees of feasibility in application.1  However, most connect to a single foundational conceptual model.4 ,5  We may someday achieve a standard operational definition for CMC. In the meantime, the work by Millar et al adds to the growing toolbox of instruments to identify CMC in populations, particularly when seeking to incorporate system and social factors within the definition. As we use these tools, it is important for us to recognize their relative strengths and weaknesses, transparently describe what was chosen and why, and seek a destination that ultimately brings value to children and families.

The authors thank Carolyn Foster and Cara Coleman for their thoughtful comments on an earlier draft of this manuscript.

Ms Gerber and Dr Coller drafted the commentary and reviewed it critically for important intellectual content; and both authors approved the final manuscript as submitted and agree to be accountable for all aspects of the work.

COMPANION PAPER: A companion to this article can be found online at www.pediatrics.org/cgi/doi/10.1542/peds.2023-064556.

FUNDING: No external funding.

CONFLICT OF INTEREST DISCLOSURES: The authors have indicated they have no potential conflicts of interest to disclose.

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