The Weekend Effect: A Patient Safety Myth?

Since the 1970’s, concerns about the risk of morbidity and mortality of patients admitted on weekends and holidays have circulated among all healthcare stakeholders.  The idea, which seems intuitive, is that care provided outside of traditional working hours is sub-par, stemming from the fact that certain services, like sub-specialty consultancy and advanced imaging techniques, tend to follow a Monday through Friday schedule.

Only in the last five years have large-scale trials offered support for the presence of this so-called “weekend effect” that has been popularized even in the lay literature.  In a landmark 2014 US study, which examined administrative data of nearly 50 million patients, the relative risk of mortality was 15% higher for patients admitted to hospitals on weekends compared to those admitted on weekdays, even after adjusting for factors like age, sex, diagnosis, race, and income level.  Another huge study, published this year, found that those patients admitted for non-elective surgery over a weekend experienced a 36% higher risk of postoperative wound dehiscence and an 8% higher risk of surgical inpatient death.

On the other hand, smaller studies regarding disease-specific surgical patients have yielded opposing results.  In studies involving thousands – not millions – of patients admitted on weekends who required urgent surgical management of appendicitis and small bowel obstruction, there was no difference in mortality between weekday and weekend admits.  Although largely systematically sound, the impact of these studies were discounted by critics who pointed to the fact that these procedures are relatively low-risk, with a much lower attendant mortality.  Overall, the medical community has thus continued to subscribe to the notion that the weekend effect reflects a true inadequacy of weekend medical services.  The effect seems so real, in fact, that the National Health Service has called for an extension of emergency hospital resources and implementation of new standards for “7-day” hospitals.  

But a study published this week in BMJ Quality and Safety seems to debunk the weekend effect theory entirely.  The authors identify a critical flaw in previous studies finding support: they had no method of controlling for severity of illness.  By using retrospective data on whether or not patients arrived to the emergency department by ambulance – a marker of illness severity shown both in their study and others to correlate with mortality – the researchers were able to identify sicker patients by those who arrived by ambulance.  

It turns out that a significantly higher percentage of patients admitted to the hospital on weekends arrived by ambulance (60% on Saturday, 61% on Sunday) compared to those admitted on weekdays (57%).  After controlling for severity of illness using this metric, their analysis, which examined over 3 million admissions to 140 hospitals in England, found no evidence that patients admitted over the weekend fared worse than those admitted on weekdays, except for an extremely small uptick in mortality for those admitted on Sunday daytime.

The authors claim that the NHS’ call for 7-day services relied on an evidence base tarnished by a consistent and problematic omission: failing to identify that patients admitted on weekends are just sicker.  Broadly speaking, the myth-busting study serves as a reminder that major policy changes should be driven by high-quality evidence, even in the context of prevailing theories that make intuitive sense.



By Nicole Van Groningen