Increased in-hospital mortality associated with weekend admission has been reported for many acute conditions, but no study has investigated "weekend effect" for acute kidney injury requiring dialysis (AKI-D). In this study, the investigators compared mortality in AKI-D patients admitted on weekday versus weekend and assessed factors associated with increased mortality.

Several studies have reported an unwanted adverse effect of weekend admission on mortality in certain acute medical conditions. Though the reason for this variation could be illness severity, some studies have hypothesized that this could be due to variation in care provided over weekends when services are a minimum. The increased mortality over weekends for certain conditions in the National Health Service (NHS) in England has led to an intense debate on reconfiguring the health service. Little is known about the impact of the weekend effect on severe acute kidney requiring dialysis (AKI-D) in England, the incidence of which has increased more than 12-foldover the past 15 years. Most nephrology departments in England provide continuous consultant cover over weekends and have the capacity to perform emergency dialysis as needed over weekends suggesting that a weekend effect is less likely to occur. Patients admitted over the weekend may present in three ways - with severe AKI requiring dialysis over the weekend, with AKI and requiring dialysis on a subsequent weekday or with no AKI, but develop AKI-D during the in-patient stay over next few days. Some studies have reported that patients starting dialysis on Sunday or a diagnosis of severe AKI over weekend, does not affect mortality, while others have reported increased mortality for AKI in all sizes of hospital over weekend. One explanation for this observation is that necessary dialysis therapy may not be initiated on a weekend as a result of limitations in physician or nurse staffing or device availability. However, bias can be created by single center studies as it is well recognized that the epidemiology of AKI-D shows considerable regional variation and this may be true for all days of the week. It can also be speculated that patients admitted on weekends may not receive optimal care resulting in development of new AKI or progression of AKI to AKI-D resulting in excess mortality.

With this background, the investigators wanted to investigate whether a weekend effect on mortality exists for AKI-D patients in England. The investigators hypothesized that patients admitted over weekend would have increased mortality irrespective of demographic features and clinical characteristics. They also hypothesized that the effect on mortality would be more pronounced in centers with no on-site nephrology services.

Inclusion Criteria:

1. AKI cases identified by using validated International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) codes of N17 in any diagnoses codes.
2. AKI cases requiring dialysis (AKI-D) were identified by OPCS code of X40.3 for hemodialysis or X40.4 for hemofiltration in any of the 24 procedures.

Exclusion Criteria:

1. Patients' with ICD10 codes N18.5 and N18.6 for chronic kidney disease stage five (CKD-5) and end stage renal disease (ESRD) respectively will be excluded.
2. Patients with OPCS-4 codes for arteriovenous fistula (L74.2) or arteriovenous shunt (L74.3) during the inpatient admission will be excluded.

2003-2015 data from the Hospital Episode Statistics (HES) database containing details of all admissions at National Health Service (NHS) hospitals in England will be used to extract all AKI-D patients

The data is anonymised and freely available from HSCIC