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The New Zealand Medical Journal

 Journal of the New Zealand Medical Association, 13-February-2009, Vol 122 No 1289

The validity of readmission rate as a marker of the quality of hospital care, and a recommendation for its definition
Juliet Rumball-Smith, Phil Hider
Abstract
Aim To perform a review of relevant literature regarding the use of readmission rate as a marker of the quality of hospital care, summarise its validity, and recommend a definition for its use.
Methods Literature search was performed on the Embase and Medline databases, with relevant articles extracted and reviewed.
Conclusions Readmission rate as a marker of the quality of hospital care has been used both internationally and nationally, although its validity has only been partially substantiated. While prone to confounding, it remains a valuable indicator due to its ease of collection and its ability to be able to be combined with other variables. Although the definition of readmission rate varies in the literature, it may be defined as ‘the number of patients who experienced unintended, acute readmission or death within 30-days of discharge from the index admission, divided by the total number of patients discharged alive within the reference period’.

The need for quality assessment and improvement in the health care system has gained increasing significance both internationally and in New Zealand.1 Numerous criteria exist for evaluating quality in hospital services, using various indicators, including readmission rate. This rate reflects the impact hospital care has had on the patient’s condition up to the point of discharge, and also represents the efficiency of the service; inpatient hospital care being a primary source of expense in the health system, and repeated admission representing a potential source of wasted resources.2
Readmission rate is collected easily by hospital information systems, and can readily be combined with information from other databases to assess the potential impact of different variables, and control for confounders.3 However, there is no agreed definition of readmission rate in the literature, with researchers and states employing multiple time periods, and failing to acknowledge subjects who died following discharge.

Methods

A literature search was undertaken on the Medline (1966–2008) and Embase (1988–2006) databases. Search terms included: ‘quality of health care’, ‘quality indicators, health care’, ‘patient readmission’, ‘readmission’, ‘rehospitalisation’, ‘readmit$’, ‘new zealand’. Searches were limited to English language material and articles with abstracts available.

Discussion

Quality in health care—Quality in health care may be defined as ‘the degree to which health services for individuals and populations increase the likelihood of desired health outcomes and are consistent with current professional knowledge’.4p4 Campbell maintains that quality can be viewed as having two simple domains, suggesting that quality of care for an individual can be defined as ‘whether individuals can access the health structures and processes of care which they need, and whether the care received is effective’.5
However, the emphasis placed on the quality of health care by the medical profession, the consumer, and the state, is relatively recent. Adverse events and incidents of ‘quality failure’ are now widely publicised. Consumers may have higher expectations of the health care they receive, and be less trusting of their provider to deliver error-free care. Health care providers need to account for resources and ensure value and efficiency of services. Funders also want to ensure that providers are meeting their expectations, and are performing adequately compared to others.
Readmission rate as an indicator of the quality of health care—Quality indicators are only one of the tools in the ‘quality toolbox’, but are indispensible in the assessment, monitoring, and improvement of the quality of patient care. Quality indicators explored in the literature include hospital multi-stay rate, length of inpatient stay, hospital mortality rates, and complication rates.6,7
The Maryland Hospital Association’s Quality Indicator Project use over 15 measurable, discrete performance indicators upon which value can be placed to describe quality.7 The wider international community has embraced the concept of quality monitoring; hospital accreditation programmes feature in over 36 countries using various indicators to ensure a minimum standard of quality.8
Readmission rate has been used as a quality indicator in various psychiatric, surgical and medical clinical specialties.9–11 It is popular as a quality indicator amongst researchers and management, for the following reasons:
  • Some early readmissions are avoidable. The proportion of preventable readmissions is widely variable in the literature, ranging from 5% to 50%, however it is agreed that the readmission rate includes a significant fraction of events of ill-health that could have possibly been avoided.12–16 Thus, the rate represents an opportunity for savings in both dollars and time, as well as the obvious benefit to the individual.11 One early study discovered that 13% of the inpatients in the United States use more than half of all hospital resources through repeated admissions.14
  • It is data that is routinely collected by most hospitals and can be compared within and between institutions. This makes it a relatively easy, fast, and inexpensive indicator to calculate.
  • Ability to be part of multivariate analysis. The combination of readmission rate and ethnicity for example, may highlight groups that are represented disproportionately and allow the development of hypotheses. Readmission rate may be able to be analysed by residential address, presence of lifestyle risk factors, or place of work. There is significant potential for future research in this area.3
  • It is an indicator that ‘transcends the inpatient wall’17p68, and provides information about standards of care provided during the admission. It assumes that provided the patient had appropriate care while admitted, was discharged in a stable condition, and had access to outpatient treatment and resources, readmission would not occur.9,18
Validity of readmission rate as an indicator of the quality of hospital care—Are those who are readmitted more likely to have experienced lower quality care? And conversely, are those who receive substandard care more likely to be readmitted?
Ashton et al. performed a significant meta-analysis of 29 comparative studies, including both hospital chart and database analyses, and in each study, process-of-care elements were examined in relation to 31-day readmission rate. The authors classified the datasets according to these elements, denoting the quality of care received as being either ‘substandard’, ‘normative’ or ‘exceptional’, when compared to accepted clinical standards of care.
After review of 13 studies, an odds ratio of readmission of 1.24 (95%CI 0.99–1.57) was calculated for those patients who received substandard as opposed to normative care. Sixteen studies were assessed to calculate a summary odds ratio comparing care of relatively low quality (‘substandard’ and ‘normative’ classification) relative to care of higher quality (studies classified as ‘exceptional’) was 1.55 (1.25–1.92), representing an increased risk of early readmission of between 25%–92% for those who experienced lower or normative quality of care.
This article represents substantial evidence for the validity of this indicator, yet is limited by the relatively few studies used to develop the odds ratios. However, this reflects the criteria for inclusion defined by the authors, such that the studies assessed were ostensibly homogeneous and provided robust results.16
Further information can be gained from cohort studies and case-control studies. Weissman et al reviewed over 1700 admissions in a case-control study, assessing the rate of 31-day readmission for patients hospitalised with pneumonia and congestive heart failure in four states of the US-trained physicians reviewed clinical records and compared the care delivered to patients subjectively, and against explicit clinical criteria. They discovered there were ‘significant but relatively small, differences in initial quality of care between patients who subsequently experienced related adverse readmissions and those who were not readmitted’.19p500, findings that were present after control for demographic and clinical variables, and hospital characteristics. Ashton also performed a case-control study of over 2000 patients who had diabetes, obstructive lung disease or heart failure, reviewing quality of inpatient care and 14-day readmission rate.
Chart review was used to ascertain quality of care, according to specified process-of-care criteria. After adjustment for demographic variables and clinical severity, they discovered a similar significant association between substandard care and subsequent unplanned readmission. This study was conducted within US Veterans Affairs Hospitals, and as such may not be able to be generalised to patients who experience financial restrictions in access to hospital care.20
However, there are few studies that have examined the second question, the issue of ‘false negatives’ in the calculation of readmission rate. This proportion represents those that receive substandard care, but due to other factors (such as death, or recovery) are not readmitted. This data is very difficult to extract, as they do not enter again into the hospital recording system, and it may be difficult to access information about the health of those in the community. Although many studies ignore the contribution of these false negatives to the validity of the readmission rate, it must be acknowledged that the validity of the rate has not been proven in this respect.21
There are other threats to the internal validity of this rate. Given that the rate is made up of a numerator (those that are readmitted to hospital within a given time period) and a denominator (total number of patients discharged alive within a reference period), intervening variables, confounders, demographic, and clinical factors may impact on both these figures.
Intervening variables can be defined as those that are ‘interposed in time in the causal sequence between the proposed independent and dependent variables’.18p1539 The most significant intervening variable for readmission rate is death in the community within the reference period, as a result of substandard care.
The impact of this variable is two-fold. Firstly, these patients are technically not eligible to be readmitted, so the overall denominator used to calculate readmission rate is artificially inflated by these absent subjects. Secondly, a patient that receives substandard care but dies in hospital or the community, or has a longer initial admission due to this quality breach, will not change the readmission rate despite substandard care.13
A confounding factor is defined as ‘a third variable that indirectly distorts the relationship between two other variables’.22 The literature discusses the following confounding factors with regards to readmission rate:
  • Disease progression: Despite optimal care, deterioration of clinical condition will increase readmission rate. In some studies, disease progression is further investigated, and readmissions due to this factor coded as ‘unpreventable’ and excluded from analysis.23
  • Post-discharge care: The quality of community care acts as an ‘inverse confounder’, in that readmission may be prevented by exceptional community care and vice versa.24 Discharge destination may also impact on the rate: for example, hospice patients are likely to be discharged ‘early’, and are unlikely to be readmitted.24 Patients who reside in nursing homes may be less likely to be readmitted as health care is more accessible.18,25
  • Readmission hospital: Readmissions may occur at other hospitals and be missed from the numerator.18
  • Ability to pay: Uninsured patients may be more likely to be discharged prematurely in health systems where there is a personal financial cost to hospital care. Similarly, different payment schemes, such as stay-based reimbursement systems may act as confounders by providing incentives to decrease length of stay but increase the number of admissions.18
  • Self-discharge: Subjects who leave hospital against medical advice cannot be assumed to have completed the treatment protocol as designed by their health professionals, thus may leave the hospital in a lesser clinical state from that intended.18
  • Demographic variables: Age, ethnicity, marital status, gender, and socioeconomic status may influence readmission rate. Whilst Ashton and Wray (1996) are not convinced these factors have been proven ‘confounders’, preferring to call them ‘moderator variables’, numerous studies have investigated the implication of individual patient variables such as age 26; 27, gender 27; 28, and even personality 29 on readmission rate.
  • Clinical variables: These factors have a greater effect on readmission rate than their demographic counterparts. Different disease processes are associated with higher risks, with diagnoses such as heart failure and diabetes increasing the risk of readmission, and medical patients being more likely to be readmitted than surgical subjects.28 Similarly, an increasing number of comorbidities and worsening severity of initial illness are associated with an increased risk of readmission.18,30 The recurrence of chronic medical conditions, and worsening functional status also act to increase readmission rate.15,27
The external validity of a quality indicator refers to its generalisability; its ability to yield comparable results over time, and at homogeneous but differing institutions. The public acceptance of the validity of readmission rate is demonstrated by its broad use. Governments and private health purchasers such as US company Blue Cross Blue Shield use it as an indicator of quality.31 The New Zealand Ministry of Health has recently added readmission rate to its performance monitoring project.32 However, while these institutions may use the rate to detail trends over time and monitor progress, there is limited external validity due to the multiple definitions of readmission rate employed among institutions and researchers.

Definition of readmission rate

‘Readmission’: Chambers and Clarke define readmission as ‘the next subsequent admission of a patient as an immediate (that is, emergency or unplanned) admission ... within a defined interval of a previous (index) discharge taking place within a defined reference period’.33p301 Ashton and Wray (1996) recommend obtaining information on the frequency of death after discharge, and state that the preferable outcome variable is “death at home or readmission within n days”. If death is the worst possible result of poor quality care, then those subjects who die within the time period should be included as part of the readmission indicator. In practice, the number of these patients is small and may change the overall indicator by a negligible amount only. However, if they are not included in the analysis then the result may be biased and produce an indicator that is an under-estimate. Accordingly, it is advised that the indicator be revised to ‘readmission or deaths’ of subjects within the specified time period.
Population: The rate is calculated by dividing the numerator (‘readmissions’) by the ‘corresponding number of patients discharged (alive) within the reference period’.33p301
Time period: Researchers in quality have employed various time periods over which readmission may occur, with intervals of between 2 weeks and 12 months used.34 As mentioned above, this variation threatens the external validity of this indicator, and makes comparison between institutions and populations difficult.
This author recommends the use of a 30-day time period:
  • A rapid review examining Medline studies in the last 10 years relating readmission rate as an indicator of quality noted that of 74 studies that defined the readmission rate in the abstract, 43% used a 1-month time period. The second most common period was 1 year or greater (19%), although these studies tended to be reviewing specific outcomes from treatment interventions.
  • The 30-day or 1-month period has been used by the government bodies of Canada, Australia, the United Kingdom, and New Zealand, to assess the quality of their health services.22,35–37
  • Analyses of the timing of readmissions demonstrate an early peak within a few weeks of discharge, which tapers off over subsequent weeks and months. Tsai et al (2001) observed that 45.7% of readmissions occurred within 5 days of discharge.38 Thus, the time period needs to be long enough to include all the information from this peak, but not so extensive that it includes data from admissions unrelated to the quality of the index stay.
  • Heggestad states that a longer time frame is associated with the inclusion of higher numbers of ‘false positives’, or unrelated admissions.34 Given the numerous factors that can impact on readmission rate, it is logical to choose a shorter time frame to minimise the influence of issues such as disease progression. Theoretically, if readmission rate is an indicator of quality of inpatient care, then the longer the time frame, the less meaningful the relationship between the two admissions. It is logical to formulate a definition that includes the data from the early peak of readmissions following discharge, but encompasses the minimum of readmissions that may be unrelated to quality issues. Some authors recommend using a 60-day interval to yield the highest possible capture of preventable readmissions, however, this must be balanced against an increasing false positive rate.34,39
The general consensus of the literature seems to be that a one-month time period provides a logical balance.14 This assumption is supported by another common indicator used to address inpatient quality, 30-day mortality rate.

Conclusion

This literature appraisal was intended to provide background information on this indicator, as such this article does not offer the same quality of information as a systematic review. However, the review notes that ‘readmission rate’ has some demonstrated internal validity and is widely used in the measurement of the quality of hospital care. It is important to recognise the limitations of this measure, and minimise the influence of possible confounding variables by way of methodological and statistical techniques. Similarly, the adoption of a consistent definition of this rate by researchers will add to its external validity and improve its generalisability. This author recommends the use of the following definition: ‘the number of patients who experienced unintended, acute readmission or death within 30-days of discharge from the index admission, divided by the total number of patients discharged alive within the reference period’.
Competing interests: None known.
Author information: Juliet M L Rumball-Smith, Research Fellow, Department of Public Health and General Practice, University of Otago, Christchurch; Phil Hider, Senior Lecturer, Department of Public Health and General Practice, University of Otago, Christchurch
Correspondence: Dr. Juliet Rumball-Smith, Research Fellow, Department of Public Health & General Practice, University of Otago, Christchurch, PO Box 4345, Christchurch, New Zealand. Fax: +64 (0)3 3643697;
email: juliet.rumball-smith@otago.ac.nz
Acknowledgements: The author acknowledges the financial assistance of the Health Research Council of New Zealand and the New Zealand College of Public Health Medicine; and supervisory support from Dr. Patrick Graham, University of Otago, Christchurch.
References:
  1. Thornley L, Logan R, Bloomfield A. Quality improvement: time for radical thought and measurable action. New Zealand Medical Journal. 2003;116(1181). http://www.nzmj.com/journal/116-1181/579
  2. Westert G, Lagoe R, Keskimaki I, et al. An international study of hospital readmissions and related utilization in Europe and the USA. Health Policy. 2002;61:269–78.
  3. Barnett R, Lauer G. Urban deprivation and public hospital admissions in Christchurch, New Zealand, 1990 - 1997. Health & Social Care in the Community. 2003;11:299–313.
  4. Institute of Medicine. Medicare: A strategy for quality assurance. Washington: National Academy Press;1990.
  5. Campbell S, Roland M, Buetow S. Defining quality of care. Social Science and Medicine. 2000;51:1611–25.
  6. Wray N, Peterson N, Souchek J, et al. The hospital multistay rate as an indicator of quality of care. Health Services Research. 1999;34:777.
  7. Kaziandijan V, Matthes N, Wicker K. Are performance indicators generic? The international experience of the Quality Indicator Project. Journal of Evaluation in Clinical Practice. 2003;9:265–76.
  8. World Health Organization. How can hospital performance be measured and monitored? Denmark: WHO Regional Office for Europe's Health Evidence Network; 2003.
  9. Lyons J, O'Mahoney M, Miller S, et al. Predicting readmission to the psychiatric hospital in a managed care environment: implications for quality indicators. American Journal of Psychiatry. 1997;154:337–40.
  10. Courtney E, Ankrett S, McCollum P. 28-Day emergency surgical re-admission rates as a clinical indicator of performance. Annals of the Royal College of Surgeons of England. 2003;85:75–8.
  11. Frankl S, Breeling J, Goldman L. Preventability of emergent hospital readmission. The American Journal of Medicine. 1991;90:667–74.
  12. Miles T, Lowe J. Are unplanned readmissions to hospital really preventable? Journal of Quality in Clinical Practice. 1999;19:211–14.
  13. Maurer P, Ballmer P. Hospital readmissions – are they predictable and avoidable? Swiss Medical Weekly. 2004;134:606–11.
  14. Benbassat J, Taragin M. Hospital readmission as a measure of quality of health care. Archives of Internal Medicine. 2000;160:1074–81.
  15. Munshi S, Lakhani D, Ageed A. Readmissions of older people to acute medical units. Nursing Older People. 2002;14:14–16.
  16. Ashton C, Del Junco D, Souchek J, et al. The association between the quality of inpatient care and early readmission: a meta-analysis of the evidence. Medical Care. 1997;35:1044–59.
  17. Franklin P., Noetscher C, Murphy M, et al. Using data to reduce hospital readmissions. Journal of Nursing Care Quality. 1999:14:67–85.
  18. Ashton C, Wray N. A conceptual framework for the study of early readmission as an indicator of quality of care. Social Science and Medicine. 1996;43:1533–41.
  19. Weissman J, Ayanian J, Chasan-Taber S, et al. Hospital readmissions and quality of care. Medical Care. 1999;37:490–501.
  20. Ashton C, Kuykendall D, Johnson M., et al. The association between quality of inpatient care and early readmission. Annals of Internal Medicine. 1995;122:415–21.
  21. Milne R, Clarke A. Can readmission rates be used as an outcome indicator? British Medical Journal. 1990;301:1139–40.
  22. New Zealand Health Technology Assessment. Acute medical admissions: a critical appraisal of the literature. Christchurch School of Medicine, Christchurch, 1998.
  23. Graham H, Livesley B. Can readmissions to a geriatric medical unit be prevented? The Lancet. 1983;321:404–6.
  24. Reed R, Pearlman R, Buchner, D. Risk factors for early unplanned readmission in the elderly. Journal of General Internal Medicine. 1991;6:223–8.
  25. Camberg,LC, Smith NE, Beaudet M, et al. Discharge destinations and repeat hospitalizations. Medical Care. 1997;35:756–67.
  26. Kossovsky M, Perneger T, Sarasin F, et al. Comparison between planned and unplanned readmissions to a department of internal medicine. Journal of Clinical Epidemiology. 1999;52:151–6.
  27. Lyratzopoulos G, Havely D, Gemmell I, et al. Factors influencing emergency medical readmission risk in a UK district general hospital: A prospective study. BMC Emergency Medicine. 2005;5:1
  28. Anderson G, Steinberg E. Hospital readmissions in the medicare population. The New England Journal of Medicine. 1984;311:1349–53.
  29. Corrigan J, Martin J. Identification of factors associated with hospital readmission and development of a predictive model. Health Services Research. 1992;27:81–101.
  30. Wong F, Ho M, Chiu I, et al. Factors contributing to hospital readmission in a Hong Kong regional hospital: a case-controlled study. Nursing Research. 2002;51:40–-9.
  31. Sabatino K, Koska M, Burke M, et al. Clinical quality initiatives: the search for meaningful - and accurate- measures. Hospitals. 1992;66:26–40.
  32. Bohm G. Principal Advisor, Quality Improvement and Audit, Ministry of Health. Personal communication to P. Hider, 3 October 2006.
  33. Chambers M, Clarke, A. Measuring readmission rates. British Medical Journal. 1990;301:1134–6.
  34. Heggestad T, Lilleeng S. Measuring readmissions: focus on the time factor. International Journal for Quality in Health Care. 2003;15:147–54.
  35. National Health Ministers' Benchmarking Working Group. First national report on health sector performance indicators: public hospitals - the state of play. Australian Institute of Health and Welfare, Canberra, 1996.
  36. Statistics Canada. Health indicators. 2004. Canadian Institute for Health Information.
  37. Dobrzanska L. Readmissions - an evaluation of reasons for unplanned readmissions of older people: A United Kingdom and international studies literature review. Quality in Ageing. 2004;December 2004.
  38. Tsai K, Lee A, Rivers P. Hospital re-admissions: an empirical analysis of quality management in Taiwan. Health Services Management Research. 2001;14:92–103.
  39. Jiminez-Puente A, Garcia-Alegria J, Gomez-Aracena J, et al. Readmission rate as an indicator of hospital performance: the case of Spain. International Journal of Technology Assessment in Health Care. 2004;20:385–91.
     
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