Numerous staging systems in medicine express both the severity and qualitative nature of pathology. The Tumor, Nodes, Metastases (TNM) system, stimulated remarkable advances in oncology, with sustained declines in death rates attributed to risk factor reduction, better screening, and improved treatments.31
We hope that disability staging, which characterizes patients by function rather than pathology, will provide a similar stimulus to advancing disability management. Similar to TNM stages, results confirm that ADL stages are capable of distinguishing among groups of elderly community-dwelling people according to 1-, 5-, and 10-year survival. Anticipated depletion of the Medicare trust fund by 201932
as the number of baby boomers eligible for Medicare benefits swells, along with increasing prevalence of ADL limitations with advanced age, high associated costs of long-term care, and looming shortages of caregivers33
all highlight the importance of being able to project trends in longevity among groups of older adults according to qualities of supportive care need. ADL stages simultaneously distinguish among groups of older adults according to the qualities of supportive care need and prognosis for survival.
The self-care tasks people can be expected to perform become clear at each stage. People at ADL 0 have no difficulty performing self-care tasks and expected survival is high. Expected 1-, 5-, and 10-year survivals decrease directly with stage. People at ADL I with “mild” ADL limitations can still perform all tasks, but are expected to have a lot of difficulty with bathing and/or walking. At ADL II, people with “moderate” limitations can no longer be expected to perform these most complex ADLs themselves. Those at ADL III have “severe” disability patterns that fall outside the typical hierarchy. They experience difficulties with the usually easiest and most fundamental self-care tasks of eating or using the toilet while retaining abilities to perform more challenging functions such as walking. At “complete” limitation ADL IV, people are unable to perform any ADLs, all self-care ability is lost, care burden is maximized, and expected survival is lowest. Our study differs from previous reports on ADL where typical counts or summation methods only characterize severity and the pattern of retained abilities is not transparent.34, 35
The 5 ADL stages continue to distinguish groups in the population by an ordered gradient of mortality after controlling for known risk factors.18–23
ADL stage remained strongly associated with death at all three time periods. Therefore, ADL stage might be applied to indicate mortality risk over and above sociodemographic factors and diagnoses. Our findings are consistent with numerous reports documenting strong associations between ADL limitations and mortality.34
The study most similar to ours was a prognostic index developed by Carey and coworkers.36
Because it included instrumental ADLs in addition to basic ADLs, it would be expected to produce a broader gradient. Their 2-year mortality was 5% for the lowest-risk group and 36% for the highest-risk group.36
In our study, 1-year mortality ranged from 2.5% for ADL 0 to 34.2% for ADL IV.
Certain predictive factors become weaker or stronger with respect to impact on short-versus longer-term mortality. Differing time-related associations were particularly notable for people at differing ADL stages. The impact of having complete ADL limitations on likelihood of mortality when compared to those with no limitations was far greater for short-than long-term suggesting that the few people at ADL IV who survived 5 or 10 years were a unique sub-group who tended to continue to survive. Time-related decrements in the association between stage and mortality also present at ADL I, II, and III compared to ADL 0, but less remarkable than for ADL IV, suggest that ADL stage, like diagnoses such as cancer, better predict shorter-than longer-term mortality. This likely relates to high short-term mortality at higher stages of limitation and to the dynamic nature of function.34, 35, 40
Intervening factors like cognitive decline determine whether people can be expected to get better, stay the same, or get worse. Stage transitions as they occur over time could reduce the strength of associations with mortality, highlighting the need for periodic reassessment.
Our study applied self-reported diagnoses and functioning, which may differ from provider assessments. Also, the patterns of mortality and survival found are only generalizable to community-dwelling elderly people; they do not necessarily reflect patterns among those in institutions. Further, observational studies are always vulnerable to unmeasured confounding factors. The data did not include a standard measure of cognition. Nevertheless, simple self- and proxy-reported diagnostic and functional status information has long been recognized as effective for stratifying community-dwelling persons according to varying mortality risk.36, 41
Moreover, all questions were extensively field tested.42
Also, people already in institutions represent a different population with needs that are distinct from those still living in the community. Finally, we adjusted for many known characteristics most associated with mortality.18–23
Future work should address stage transitions and associations with other outcomes.
Stages might be applied to project 1-, 5-, and 10-year survival in the aging US population. Constructed to reflect the profile of care needs of survivors, stages are easily determined, requiring only individuals’ (or, when necessary, close proxy) answers to simple questions about difficulties experienced in performing each activity. Application of stages to patient screening during outpatient visits or homecare might capture early ADL problems while still treatable. Moreover, stratification by stage could aid researchers or policy makers in testing alternative disability management strategies and projecting needs for rehabilitative, supportive, and long-term care in the aging population. The impact of those strategies might be assessed relative to stage-specific survival. ADL stages, by placing a ceiling on the maximum amount of difficulty an individual can experience with each of the 6 ADLs along with estimated survival time, could prove beneficial in planning for the functional assistance and supportive aspects of care for the population.