Mohammed et al. BMC Health Services Research 2012, 12:87 http://www.biomedcentral.com/1472-6963/12/87 RESEARCHARTICLE Open Access Weekend admission to hospital has a higher risk of death in the elective setting than in the emergency setting: a retrospective database study of national health service hospitals in England Mohammed A Mohammed1*, Khesh S Sidhu2, Gavin Rudge3 and Andrew J Stevens3 Abstract Background: Although acute hospitals offer a twenty-four hour seven day a week service levels of staffing are lower over the weekends and some health care processes may be less readily available over the weekend. Whilst it is thought that emergency admission to hospital on the weekend is associated with an increased risk of death, the extent to which this applies to elective admissions is less well known. We investigated the risk of death in elective and elective patients admitted over the weekend versus the weekdays. Methods: Retrospective statistical analysis of routinely collected acute hospital admissions in England, involving all patient discharges from all acute hospitals in England over a year (April 2008-March 2009), using a logistic regression model which adjusted for a range of patient case-mix variables, seasonality and admission over a weekend separately for elective and emergency (but excluding zero day stay emergency admissions discharged alive) admissions. Results: Of the 1,535,267 elective admissions, 91.7% (1,407,705) were admitted on the weekday and 8.3% (127,562) were admitted on the weekend. The mortality following weekday admission was 0.52% (7,276/1,407,705) compared with 0.77% (986/127,562) following weekend admission. Of the 3,105,249 emergency admissions, 76.3% (2,369,316) were admitted on the weekday and 23.7% (735,933) were admitted on the weekend. The mortality following emergency weekday admission was 6.53% (154,761/2,369,316) compared to 7.06% (51,922/735,933) following weekend admission. After case-mix adjustment, weekend admissions were associated with an increased risk of death, especially in the elective setting (elective Odds Ratio: 1.32, 95% Confidence Interval 1.23 to 1.41); vs emergency Odds Ratio: 1.09, 95% Confidence Interval 1.05 to 1.13). Conclusions: Weekend admission appears to be an independent risk factor for dying in hospital and this risk is more pronounced in the elective setting. Given the planned nature of elective admissions, as opposed to the unplanned nature of emergency admissions, it would seem less likely that this increased risk in the elective setting is attributable to unobserved patient risk factors. Further work to understand the relationship between weekend processes of care and mortality, especially in the elective setting, is required. * Correspondence: [email protected] 1Primary Care Clinical Sciences, University of Birmingham, Birmingham, England, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK Full list of author information is available at the end of the article © 2012 Mohammed et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Mohammed et al. BMC Health Services Research 2012, 12:87 Page 2 of 10 http://www.biomedcentral.com/1472-6963/12/87 Background AdmissionsonaSaturdayorSundaywereclassedas Although acute hospitals offer a twenty-four hour seven weekend admissions and admissions during Monday to day a week service, it is known that levels (seniority and Friday were classed as weekday admissions. The HES numbers) of staffing are lower over the weekends than data source does not include time of admission. on weekdays [1]. Consequently health care processes Our approach was to consider elective and emergency within hospitals, such as diagnostic testing or advice admissions separately. For emergency cases, as recom- from senior colleagues, may be less readily available mended by Jones, [15] we excluded admissions dis- over the weekend [2]. This “weekend phenomenon” charged alive with a zero day length of stay, because in reflects a planned reduction in elective activity as well England such episodes of care are likely to be an artefact as the notion that weekend working is unpopular of the NHS drive to reduce Accident & Emergency wait- amongst staff and some staff only have weekday working ing times rather than reflecting any specific clinical or contracts [3]. Typically, consultants will work one week- epidemiological phenomenon [15]. end in four or five in English hospitals [1]. Whilst some of the operational reasons behind the Data weekend phenomenon may be justifiable, there appears For each discharge episode, we obtained the patient’s to be some concern that outcomes for patients admitted age, gender, date of admission, date of discharge, dis- over the weekend may be less favourable than patients charged alive/dead and the Healthcare Resource Group admitted during the weekday [2,4] This association (HRG) version 3.5. HRGs are standard groupings of between weekend admission and outcome has been clinically similar treatments which use common levels of termed the “weekend effect”[5]. Evidence for such con- healthcare resource [16]. They work in a similar way to cern appears to stem from a few studies which have the Diagnostic Related Groups [17] used in the United found adverse outcomes for weekend admissions [5-13]; States and other healthcare systems primarily to support but these studies have, in general, focused primarily on financial reimbursement to healthcare providers. We emergency admissions, have been limited to specific used HRG version 3.5 developed for the NHS to deter- well defined conditions (eg stroke, myocardial infarction, mine if the patient was a complex elderly patient (14/ aortic aneurism, chronic obstructive pulmonary disease) 610 HRG codes ending in “99”) and if the patient had and/or settings (eg internal medicine, intensive care complications and/or comorbidities (119/610 HRG units, teaching hospital status). Nevertheless, unlike codes that include “with cc” in their description). These much of the previous work, we were interested in the “withcc” HRG codes can sometimes include an age cri- extent to which weekend admission was associated with terion (eg aged > 69 Each admission record in the an increased risk of death for elective admissions sepa- administrative HES data includes International Classifi- rately from emergency admissions. A key justification cation of Disease (ICD)-10 diagnoses, (one primary diag- for our work is that the mechanism which results in a nosis and up to 19 secondary diagnoses) and procedures weekend admission in the elective setting is a “planned” coded by the Office of Population Censuses and Surveys process, which is much more amenable to change (OPCS-4) coding system, (up to a maximum of 24 per because the process is primarily designed and owned by admission) which are parsed through a HRG grouping the hospital, whilst in the emergency setting the admis- algorithmtoderivetheHRGforagivehospital sion is “unplanned”, and the underlying process is less admission. amenable to change because of the complex interplay The following HES records were excluded - day cases, with out-of-hours primary care, patient behaviors and patients aged less than 16 years of age on admission, ambulance services, making a pooled analysis less justifi- episodes of care relating to maternity care (because this able. We used admission data from all acute hospitals in is a 24 h service), mental health episodes of care other the National Health Service (NHS) in England to further than dementia (because mental health admissions are investigate this question. predominantly to psychiatric health hospitals). Method Descriptive statistics We undertook a retrospective desktop statistical analysis We compared the case-mix profile, mortality and length based on all patient discharges during the year April of stay of patients admitted over the weekend and week- 2008 to March 2009 from all acute hospitals (n = 328, day for elective and emergency admissions using comprising 221 NHS Trusts) in England. The discharges descriptive statistics. Using run charts we explored the were obtained via Hospital Episode Statistics [14] (HES), pattern over time (month) of mortality for admissions a routinely collected national dataset of patients on weekends and weekdays to determine if there were admitted for care used by the NHS in England. any substantial time dependent effects (eg seasonality). Mohammed et al. BMC Health Services Research 2012, 12:87 Page 3 of 10 http://www.biomedcentral.com/1472-6963/12/87 These descriptive analyses were also used to inform the less than 0.7 are considered to show poor discrimina- development of a subsequent logistic regression model. tion, values of 0.7-0.8 can be described as reasonable, and values above 0.8 suggest good discrimination. Cali- Statistical model bration, the accuracy of risk predictions, was tested We developed two logistic regression models with death using the deciles of risk table described by Hosmer and in hospital as the response variable and with a binary Lemeshow, where the overall difference between weekend admission variable whilst controlling for the expected and observed numbers of death for each decile covariates shown in Table 1. The elective and emer- of risk is compared using a c2-test with 8 degrees of gency models