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Lower Extremity Performance in Nondisabled Older Persons as a Predictor of Subsequent Hospitalization

^a Epidemiology, Demography, and Biometry Program, National Institute on Aging, National Institutes of Health, Bethesda, Maryland
^b Sticht Center on Aging, Wake Forest University School of Medicine, Winston-Salem, North Carolina
^c Geriatric Department, I Fraticini, National Research Institute (INRCA), Florence, Italy
^d Department of Health Sciences, University of Jyväskylä, Finland

Brenda W.J.H. Penninx, Sticht Center on Aging, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157 E-mail: bpenninx{at}wfubmc.edu.

William B. Ershler, MD

	Abstract

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Background.

This study examines, in initially nondisabled older persons, the impact of reduced lower extremity performance on subsequent hospitalizations.

Methods.

A 4-year prospective cohort study was conducted among 3381 persons, aged 71 years and older, who initially reported no disability. At baseline, lower extremity performance was measured by an assessment of standing balance, a timed 2.4-m walk, and a timed test of rising from a chair five times. Data on subsequent hospital admissions and discharge diagnoses over 4 years were obtained from the Medicare database.

Results.

During the follow-up period, nondisabled persons with poor lower extremity performance spent significantly more days in the hospital (17.7 days) than those with intermediate and high performance (11.6 and 9.7 days, respectively). Poor lower extremity performance in nondisabled persons significantly predicted subsequent hospitalization over 4 years (relative risk for hospitalization in those with poor vs high performance: 1.78; 95% confidence interval, 1.45–2.17). This increased hospitalization risk could not be explained by several indicators of baseline health status. Increased hospitalization risks were especially found for geriatric conditions, such as dementia, decubitus ulcer, hip fractures, other fractures, pneumonia, dehydration, and acute infections.

Conclusions.

Even in persons who are currently nondisabled, a simple measure of lower extremity performance is predictive of subsequent hospitalization, especially for geriatric conditions.

EVALUATION of physical functioning using objective performance tests may play a valuable role in clinical geriatrics as well as in aging research. Poor lower extremity performance in nondisabled older persons, as measured by tests of walking, balance, and chair stands, has been found to be associated with poor health status, physiological alterations, such as low albumin and hemoglobin levels, poor muscle strength, obesity, and physical inactivity ^(1)(2)(3)(4). These findings support the view that low physical performance may reflect a state of preclinical disability, a precursor state characterized by the presence of functional impairments and limitations that have not yet caused disability ⁽⁵⁾.

Measures of lower extremity performance are strong predictors of adverse health outcomes, even in nondisabled older persons. Longitudinal studies have shown that nondisabled older people with poor scores on lower extremity performance tests were at much higher risk for subsequent disability than those with high scores ^(6)(7)(8). Also, other adverse health outcomes, such as institutionalization and mortality, are strongly predicted by poor lower extremity performance ^(9)(10). These findings suggest that poor lower extremity performance could be a good assessment method to identify older persons who are not currently disabled but who are at increased risk for subsequent deterioration in their health status.

However, the outcomes studied so far (i.e., disability, institutionalization, and mortality) are rather broad endpoints and do not yield much insight into the actual events leading from poor performance to these outcomes. A recent study showed that a substantial proportion of older persons are hospitalized during the year when they become severely disabled ⁽¹¹⁾. Further understanding of the pathway by which poor performance leads to disability and mortality could be offered by further examination of hospital discharge diagnoses. So far, however, no studies have yet explored which specific hospital discharge diagnoses are most likely to occur in older persons with poor lower extremity performance. This study prospectively examines poor lower extremity performance in nondisabled older persons as a risk factor for subsequent hospitalization over 4 years.

	Methods

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Study Population
Data for this study are from three communities of the Established Populations for Epidemiologic Studies of the Elderly (EPESE). The sampling design and data collection methods have been described in detail previously ⁽¹²⁾. More than 10,000 community-dwelling men and women aged 65 years and older were interviewed between 1981 and 1983 in East Boston, Massachusetts; New Haven, Connecticut; and Iowa and Washington counties in rural Iowa. Follow-up interviews were conducted annually for 6 years. A total of 5174 persons received a personal in-home interview at the sixth follow-up in 1988. This follow-up assessment is considered the baseline for this study, as this was the first assessment that included physical performance measures. Because of missing data on the performance tests, 100 persons (1.9%) were excluded. Because the present study aims to examine the intermediate health outcomes that may be implicated in the pathway leading to disability and other adverse events, an initially nondisabled cohort was selected. Therefore, 1422 participants who reported disability in activities of daily living (difficulty with transferring from bed to a chair, using the toilet, bathing, or walking across a room) or mobility (difficulty with walking 1/4 mile or climbing stairs) were excluded. Because disability is also to be expected in participants who were unable to complete one or more of the performance tests (summary performance score 3, described later), another 236 persons were excluded from the study population. Of the remaining 3416 subjects, 35 subjects (1.0%) were excluded because they could not be matched to the Medicare Provider Analysis and Review (MEDPAR) database, which contains hospital discharge information on all persons covered by the Medicare Program Part A, leaving 3381 subjects for the analyses.

Measurements
Lower extremity performance.-- Lower extremity performance was measured by an assessment of standing balance, a timed 2.4-m walk, and a timed test of 5 repetitions of rising from a chair and sitting down. For testing standing balance, subjects attempted to maintain their balance for 10 seconds in progressively more challenging positions. The classification is as follows: unable, 0; able to hold side-by-side position but unable to hold semitandem position (heel of one foot beside big toe of other foot) for 10 s, 1; able to hold semitandem position for 10 seconds but unable to hold full tandem position (heel of one foot in front of other foot) for 3 or more seconds, 2; able to stand in full tandem position for 3 to 9 seconds, 3; and able to maintain full tandem position for 10 seconds, 4. To test walking speed, a 2.4-m (8-ft) walk at the subject's normal pace was timed twice, and the faster of the two walks was scored according to quartiles of the time required in three EPESE populations ⁽⁹⁾. Categories were as follows: unable, 0; 5.7 seconds or more, 1; 4.1 to 5.6 seconds, 2; 3.2 to 4.0 seconds, 3; and 3.1 seconds or less, 4. For testing the ability to rise from a chair, subjects were asked to fold their arms across their chests and to stand up from a sitting position and sit down five times as quickly as possible. Categories, based on quartiles of the time required in the three EPESE populations, were as follows: unable, 0; 16.7 seconds or more, 1; 13.7 to 16.6 seconds, 2; 11.2 to 13.6 seconds, 3; and 11.1 seconds or less, 4.

For the three tests, high test-retest reliability has been demonstrated ^(2)(13)(14). As in previous publications (e.g., [6,9]), a summary index of lower extremity performance was developed by summing scores of the three tests. For the present study, the nondisabled study population was divided into three levels of lower extremity performance: low performance (summary score 4–6), intermediate performance (summary score 7–9), and high performance (summary score 10–12).

Subsequent hospital admissions.-- Data on hospital admissions that took place over the 4 years after the assessment of performance were obtained from the MEDPAR database, which contains information on all persons covered by the Medicare Program Part A (97% of the US population aged 65 years and older). Hospitalizations were considered only if they were not admissions to skilled nursing facilities. Discharge diagnoses were coded according to the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM, ⁽¹⁵⁾). Participants were classified as having no or one or more hospitalizations during follow-up. In addition to this, specific common conditions were considered and divided into three general categories. Acute conditions included acute myocardial infarction (410.0–410.9), stroke (430.0–432.9, 434, 436), and gastrointestinal hemorrhage (578.0–578.9, 531.0, 531.2, 531.4, 531.6, 532.0, 532.2, 532.4, 532.6, 533,0, 533.2, 533.4, 533.6). Chronic conditions included angina pectoris (413.0–413.9), congestive heart failure (428.0–428.9), peripheral artery disease (443.9, 444.22), cancer (140.0–212.9), diabetes (250.0–250.9), chronic obstructive pulmonary disease (COPD; 490.0–496.9), and Parkinson's disease (332.0). Geriatric conditions, which can be considered to be generally associated with frailty, included dementia (290.0–290.9, 294.1, 294.9), decubitus ulcer (707.0), hip fracture (820.0–821.9), all other fractures (800.0–819.9, 822.0, 929.9), pneumonia (480.0–486.9, 507.0), dehydration or electrolytes problems (276.0, 276.5, 276.9), deep venous thrombosis (451.1, 451.11, 451.19, 451.81, 453.2), pulmonary embolism (415.1), acute infections (defined as infections that are usually completely cured in less than 1 month), and chronic infections (defined as infections that usually last more than 1 month). ICD-9-CM codes used to define acute and chronic infections are available on request.

Baseline health status.-- Specific conditions were considered present at baseline when a hospital discharge diagnosis for that condition was found in the 3 years prior to baseline (between 1985 and 1988). In addition, the participants were asked annually during interviews, prior to our baseline measurement (between 1982 and 1988), whether they were told by a doctor that they had diabetes, heart attack, stroke, hip fracture, or cancer. For these conditions, either self-report or a previous hospital discharge diagnosis was considered to be evidence for presence at baseline. In our analyses, we adjusted only for prevalent diseases that were associated with lower extremity performance in our nondisabled population ⁽¹⁾, which were stroke, hip fracture, diabetes, myocardial infarction, COPD, and acute infections. Body mass index (BMI), which is also associated with performance in our study, was computed as weight in kilograms divided by the square of height in meters from self-reported data. In addition, blood samples were collected at baseline in a nonfasting state at participants' homes and processed by a commercial laboratory (Nichols Institute, San Juan Capistrano, CA). Five tests were associated with lower extremity performance in our nondisabled sample ⁽¹⁾ and will be used here: albumin (g/dl), hemoglobin (g/dl), leukocyte count (10³/µl), glucose (mg/dl), and -glutamyl transferase (g/dl).

Statistical Analyses
Differences across lower extremity performance groups (low, intermediate, and high) in age, sex, deaths, and number of hospital admissions and hospital days during follow-up were determined. Cox proportional hazards regression models were used to calculate the relative risks for becoming hospitalized and for dying during follow-up across the three levels of lower extremity performance, after adjustment for age, sex, and measures of baseline health status. For each specific hospital discharge diagnosis, the occurrence over 4 years was compared across the three levels of lower extremity performance. Statistically significant differences were tested using logistic regression analyses adjusted for age and sex. Cox proportional hazards regression analyses were performed to compare the time to first occurrence of each specific hospital discharge diagnosis across the levels of lower extremity performance function. Subjects who did not have a report of that specific hospital discharge diagnosis were censored at December 31, 1992, or at time of death, whichever came first. To obtain summary estimates across the three communities, models were stratified by community using the STRATA option of SPSS COXREG (SPSS Inc., Chicago, IL) procedure. Relative risks (RRs) and 95% confidence intervals (CIs), adjusted for age, sex, and number of hospitalizations, were used as the measures of association to indicate the risk of subsequent hospitalization for the specific discharge diagnosis in persons with low and intermediate performance, when compared with persons with high performance.

	Results

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The initially nondisabled population in this study consisted of 2031 women (60.1%) and 1350 men, with a mean age of 77.2 years (range, 70–95 years). Of these 3381 nondisabled participants, 627 (18.5%) had a low level of lower extremity performance, 1413 (41.8%) had intermediate performance, and 1341 (39.7%) had high performance. Subjects with low performance were older, more often female, more often hospitalized during follow-up, had more hospital days during follow-up, and had a higher mortality rate than those with intermediate and high performance (Table 1 , all p < .001). During 4 years of follow-up, the mean number of hospital days was 17.7 in persons with low performance and 11.6 and 9.7 in those with intermediate and high performance, respectively.

View larger version (13K): [in this window] [in a new window]   Figure 1. Relative risks for hospitalization and death in initially nondisabled older persons with low and intermediate levels of lower extremity performance compared with persons with high levels, after successive inclusion of adjustment variables. Relative risks (RR; indicated by symbols) and 95% confidence intervals (indicated by the lines) are from Cox proportional hazards regression analyses. • denotes the relative risk after adjustment for sex and age; denotes the relative risk after additional adjustment for BMI, baseline stroke, hip fracture, diabetes, myocardial infarction, chronic obstructive pulmonary disease, and acute infections. denotes the relative risk after additional adjustment for serum levels of hemoglobin, leukocytes, glucose, albumin, and -glutamyl transferase.

For acute catastrophic conditions like myocardial infarction, stroke, and gastrointestinal hemorrhage, no association with lower extremity performance could be found (Table 2 ). For the chronic conditions, hospital discharge diagnosis for congestive heart failure, diabetes, and COPD occurred more often in those with poor performance. Interestingly, lower extremity performance was associated with several geriatric conditions in older persons. When compared with subjects with higher performance scores, those with low performance more often had discharge diagnoses for dementia, decubitus ulcer, hip fractures, pneumonia, dehydration, and acute infections (all p values for trend <.05).

View larger version (17K): [in this window] [in a new window]   Figure 2. Cumulative incidence of discharge diagnoses for geriatric conditions across level of lower extremity performance in initially nondisabled older persons. Geriatric conditions include dementia, decubitus ulcer, fractures (hip or others), pneumonia, dehydration, deep venous thrombosis, pulmonary embolism, and infections (acute or chronic).

For each discharge diagnosis that was associated with lower extremity performance, we repeated the Cox proportional hazard regression analyses, after excluding the persons with baseline presence of that condition. In persons with no prevalent diabetes, poor lower extremity performance did not increase the risk of subsequent hospitalization for diabetes (RR = 0.84; 95% CI = 0.43–1.63). For all other conditions, exclusion of the persons with baseline presence of that condition did not substantially change the relative risks, and all relative risks remained statistically significant (data not shown).

	Discussion

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In this study among nondisabled persons aged 71 years and older, lower extremity performance was measured using simple objective tests involving gait, balance, and ability to rise from a chair. These tests were strongly predictive of subsequent hospitalization and mortality, even after adjustment for several baseline chronic conditions and physiological parameters. Poor lower extremity performance was especially predictive of hospitalization for geriatric conditions. Nondisabled older persons with poor performance were significantly more likely to be hospitalized with diagnoses of dementia, decubitus ulcer, hip fractures, other fractures, pneumonia, dehydration, and acute infections than those with high performance.

Why does poor lower extremity performance in a nondisabled older population predict subsequent hospitalization? Objective tests of physical performance probably capture more information than presence of chronic conditions or physiological alterations alone. For instance, aspects such as severity of disease, disuse unrelated to disease status, health behaviors, and sense of well-being and motivation could also influence a person's score on performance tests. In addition, level of fitness and physical activity are important determinants of physical performance. All these aspects may explain why, after adjustment for disease presence and physiological alterations, lower extremity performance remained an independent and strong predictor of hospitalization and mortality in our study. Consistent with this, Tinetti and Ginter ⁽¹⁶⁾ demonstrated that performance testing of mobility provided information that was not ascertained in a standard neuromuscular examination. Guralnik also showed evidence that lower extremity performance measures complement self-report disability measures in providing useful information about functional status ⁽⁹⁾.

Because the present study population consisted of older persons who did not yet report disability, it is very likely that lower extremity performance predicts subsequent adverse health outcomes in large part because it reflects underlying health status changes and physiological decline that have not yet caused frank disability. Fried and Guralnik ⁽¹⁷⁾ showed that individuals may be somewhat compromised functionally as a result of underlying health status changes, but may be able to compensate for this compromise and function at a satisfactory level. Thus, in a nondisabled older population, poor lower extremity performance may reveal a preclinical state of decreased function for which the individual has made adequate adaptations to maintain daily activities.

Medicare hospital discharge records were used to describe subsequent health events of poor lower extremity performance in order to gain insight into the pathway leading to disability and mortality. It should be noted that, in general, temporal sequence cannot be completely ascertained with our data. For example, some of the health outcomes examined, such as decubitus ulcer, occur subsequent to disablement. In addition, for some long-standing chronic progressive conditions, such as diabetes and COPD, it is likely that the presence of these conditions had already been causing poor levels of lower extremity performance prior to hospitalization. The increased hospitalization risks for these conditions in persons with low performance may simply be explained by the fact that poor lower extremity performance was already a reflection of a more severe stage of these conditions. This seemed to be the case for diabetes, because poor performance predicted subsequent hospitalization for diabetes among persons with diabetes at baseline, but not among those without diabetes at baseline. For all other conditions, however, excluding persons with baseline presence of the condition did not substantially change the results, and all relative risks remained statistically significant.

Our results showed that poor performance was not a significant predictor for hospitalizations for several acute and chronic conditions, such as myocardial infarction, stroke, congestive heart failure, angina, and cancer. However, poor performance was strongly predictive of hospitalizations for geriatric conditions such as dementia, decubitus ulcer, hip and other fractures, pneumonia, dehydration, and infections. This suggests that, unlike a specific diagnosis, poor lower extremity performance more accurately reflects a state of general vulnerability for various adverse geriatric conditions. Tinetti and coworkers ⁽¹⁸⁾ also demonstrated that functional dependency reflects impairments in multiple organ systems more than a specific disease or diagnosis. These findings support the idea that there may be a preclinical state of disability that indicates risk of general decline into a state that can be thought of as frailty, which can be defined as a state of reduced physiological reserve associated with an increased general susceptibility for disability and health deterioration ^(19)(20)(21). Lower extremity performance assessment might be a valuable screening test for risk of future development of frailty. Our results show that this assessment is able to identify initially nondisabled older persons who are vulnerable for various adverse frailty-related geriatric conditions.

A limitation of this study was that subsequent health outcomes were identified only through diagnoses listed on hospital discharge records. Consequently, information about conditions that seldom require hospitalization, such as arthritis, was unavailable in this study. In addition, information is only present for conditions that were severe enough to require hospitalization. Also, because persons with low performance had higher hospitalization rates than those with high performance, they had a greater chance of bringing health conditions to the attention of the physician, while being hospitalized for another condition. However, adjustment for the number of hospital admissions during follow-up had a very small effect on the results, which suggests that such a potential ascertainment bias was of limited influence in our study.

Our findings are relevant for those planning interventions aimed at preventing health deterioration in old age. The process of health deterioration and disablement in the older population is often described as a complex sequence of events in which advancing age, multiple chronic conditions, and physiological decrements play a role, without one clear underlying cause ⁽¹⁹⁾. Consequently, for many older individuals with comorbidity and complex problems, targeting a single risk factor has little value. An alternative approach is to directly target common factors that increase the risk of adverse health outcomes, regardless of specific causes. Our findings show that poor lower extremity function could be a good target for this. A number of studies have shown that interventions are able to improve characteristics such as strength, gait, and balance ^{(22)(23)(24)(25)}. Future prospective clinical trials should address clinically relevant approaches to intervening in older persons with such preclinical changes in functioning.

Performance assessment is not meant to replace disease status as a prognosticator of future adverse events. However, it may be a valuable addition to a clinician's assessment because it appears to contribute prognostic information beyond that obtained from standard indicators of health status. Lower extremity performance assessment may be a suitable instrument for identifying older persons "at risk" for subsequent adverse events, especially those related to frailty. Further investigation is needed in clinical settings, because the prognostic value of performance measures in assessing requirements for care of an individual patient cannot be inferred from population studies alone.

	Acknowledgments

 
This study was supported by the National Institute on Aging ([NIA] contracts N01-AG-0215, N01-AG-02106, and N01-AG-02107). This study was completed when Dr. Penninx was a Visiting Scientist at the NIA.

Received August 6, 1999

Accepted February 9, 2000

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