A new study has found that “patients are more likely to die in hospital if they are admitted at the weekend”, according to BBC News. The broadcaster said the research backs up previous studies suggesting patients admitted to hospital at the weekend have a lower chance of survival.
The new study in question looked at over 14 million admissions to English NHS hospitals over the financial year of 2009/10. Researchers looked at risk of patients dying from any cause within 30 days of admission taking into account various other factors that could influence the risk, such as age, reason for admission, and other medical illnesses.
During the year there were 187,337 deaths that occurred within 30 days of admission, equating to 1.3% of all those hospitalised. When they looked at factors associated with risk they found a person admitted on a Sunday had 16% increased risk of dying following admission compared to a person admitted on a Wednesday. Conversely, patients were more likely to die on a mid-week day rather than a Saturday or Sunday.
While the study has found a pattern relating to admission day and the risk of dying, the reasons for this are unknown and it should not be assumed that the pattern is due to staffing levels or the availability of senior staff. There could be various reasons for the relationship. For example, it may be that people who need to see the doctor and be admitted on a weekend have more severe illness than people who would wait until the following Monday to be admitted.
While this very large study found a pattern, it will take further delving to unlock the reasons why, which are likely to be more complex than simply the availability of staff.
Where did the story come from?
This study was authored by researchers from University College London and various other institutions in the UK. The study was published in the Journal of the Royal Society of Medicine and received no outside funding.
What kind of research was this?
This was a retrospective cohort study aiming to see if being admitted at the weekend carried a higher risk of mortality than admission on a weekday. To do so the researchers looked at all hospital admissions that occurred within the NHS over the 2009/10 financial year. It was concerned with ‘30-day mortality’, that is, deaths occurring within 30 days of a hospital admission (either in or out of hospital).
The researchers adjusted their analysis to account for various factors that could have affected this risk, but do not describe how the severity of patients’ conditions was taken into account. This means it is difficult to tell how effectively this potentially major confounder has been accounted for. The severity of a patient’s illness, the type of care provided to them and the differences in their outcome are likely to relate to each other in complex ways, and so the topic will need further careful analysis.
What did the research involve?
The researchers analysed all admissions to the English National Health Service (NHS) during the financial year 2009/10. They linked admission records to official mortality data from the Office of National Statistics to identify all deaths that occurred within the 30 days following an admission (both those occurring in or out of hospital).
Using their data the researchers then developed statistical models to account for risk of death following admission. In their main model they adjusted for factors that were likely to have a strong effect on mortality risk:
- whether or not the admission was an emergency
- source of admission (for example, from home or transfer from another hospital)
- number of previous emergency admissions
- number of previous ‘complex’ admissions
- medical co-morbidities
- social deprivation
- hospital trust
- day of the year (seasonality)
- day of the week admission occurred on
They looked at both risk associated with being admitted over the weekend, and with staying in hospital over the weekend (admitted during the week but being an inpatient over the weekend).
What were the basic results?
There were 15,061,472 admissions to the NHS in England over this one-year period, and the researchers had information on 30-day mortality and other patient characteristics for 14,217,640 of them (95% of all admissions). There were 187,337 deaths in hospital within 30 days of admission. Admission on weekend days was associated with an increased risk of 30-day death compared with admission on weekdays:
- Sunday admissions were associated with a 16% increased risk compared to those on a Wednesday (hazard ratio [HR] 1.16, 95% confidence interval [CI] 1.14 to 1.18)
- Saturday admissions were associated with an 11% greater risk versus Wednesday admissions (HR 1.11, 95% CI 1.09 to 1.13)
Conversely, deaths were more likely to occur during the week than at the weekend. Staying in hospital on a Sunday was associated with a slightly lower risk of death than staying in hospital on a Wednesday (HR 0.92, 95% CI 0.91 to 0.94), as was staying in hospital on a Saturday (HR 0.95, 95% CI 0.93 to 0.96).
There were 284,852 deaths overall – both in an out of hospital – and 34% of people that died did so after they had been discharged from hospital. Results for the researchers’ subsequent model, examining all deaths, not just those occurring in a hospital, were similar.
How did the researchers interpret the results?
The researchers conclude that admission to hospital at the weekend is associated with increased risk of dying within 30 days of admission. However, death is more likely to occur on a mid-week day than a weekend.
The main finding of this study was that being admitted to hospital at the weekend (Saturday or Sunday) is associated with a significant increased risk of death over the following 30 days. This study has strengths in that it has used an extremely large and reliable data set representative of almost all hospital admissions within the NHS in England during one financial year. The researchers’ model also accounted for a wide range of medical and sociodemographic factors and characteristics of admission that could have influenced the risk of death.
While the researchers’ models adjusted for a variety of important confounders, it is difficult to see from the report how they did this, making it difficult to decide whether all relevant factors have been appropriately adjusted for. Most importantly, this study has not examined the reasons why there may be increased risk of death with weekend admission, so no assumptions should be drawn about staffing levels or the availability of senior staff.
It is important to be aware that an increased risk of subsequent death of 16% (Sunday compared to Wednesday) is a relative measure, representing an increase of only about two extra deaths for every 1,000 people admitted on a weekend compared to a week day (a x 0.16 relative increase beyond a 13 per 1,000 average baseline risk of death).
The researchers do offer some potential reasons for the patterns seen, putting forward the hypothesis that patients admitted at the weekend may include patients whose illness may have been severe enough to justify not waiting until a week day, while those who were less ill may have waited rather than going to the hospital at the weekend.
This is an interesting and indeed plausible theory but it is not clear how the researchers adjusted severity of illness in their analysis, and therefore it is not possible to confirm if this phenomenon accounts for the small absolute difference in deaths seen.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
Daily Mail, 2 February 2012
The Guardian, 2 February 2012
Metro, 2 February 2012
Links to the science
Journal of the Royal Society of Medicine. Published online on February 2 2012