The increased mortality associated with a weekend emergency admission is due to increased illness severity and altered case-mix.

BACKGROUND: A weekend emergency medical admission has been associated with a higher mortality. We have examined all weekend admissions to St James' Hospital, Dublin between 2002 and 2009.
METHODS: We divided admissions by weekday or weekend (Saturday or Sunday) presentation. We utilised a multivariate logistic model, to determine whether a weekend admission was independently predictive of 30 day outcome.
RESULTS: There were 49337 episodes recorded in 25883 patients; 30-day inhospital mortality at the weekend (9.9% vs. 9.0%) had an unadjusted Odds Ratio of 1.11 (95% CI 0.99, 1.23: p=0.057). In the full risk unlike the univariate) model, a weekend admission was not independently predictive (OR 1.05; 95% CI: 0.88, 1.24). The case-mix for a weekend admission differed; with more neurological diagnoses (22.8% vs 20.4% : p = 0.001) and less gastrointestinal disease (18.3% vs 21.1% : p = 0.001). A biochemistry only illness severity score predicted a higher mortality for weekend admissions.
CONCLUSION: Patients admitted at the weekend had an approximate 11% increased 30-day in-hospital mortality, compared with a weekday admission. However, admission at the weekend was not independently predictive in a risk model that included Illness Severity (age and biochemical markers) and co-morbidity. Sicker patients, with a worse outcome, are admitted over the weekend; these considerations should inform the allocation of healthcare resources.