Defining Acute Kidney Injury Episodes

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Gareth Davies
Tim Scale
Ashley Akbari
James Chess
Ronan A Lyons


Acute Kidney Injury (AKI) is a common, serious condition effecting up to 20% of all hospital admissions in the UK. AKI has an agreed definition for its recognition, however there is no consensus for the duration of an AKI episode.

Objectives and Approach
We aimed to describe four different potential definitions of an AKI episode. AKI was identified using an SQL (Structured Query Language) based algorithm (an implementation of the NHS England eAlert algorithm) applied to serum creatinine (SCr) results from a South Wales population of ~518,000 people, held in the Secure Anonymised Information Linkage (SAIL) Databank. Using a person’s index AKI case, we applied four different rules to define an episode of AKI. These definitions are: ALERTS - until they no longer trigger an AKI eAlert, 90 DAYS - until 90 days post first AKI test and <1.2/<1.5 until the SCr recovers to <1.2 or 1.5 times their baseline creatinine.

There were 1,832,122 SCr tests in 340,908 people between 2011-2013, of which 93,843 were alerts (5.12%). This fell to 81,948 alerts in 21,979 patients when dialysis and transplant patients were excluded. Of these patients with AKI 7,792 (35.5%) were dead at 1 year after their first episode. There were 31,482, 33,758, 26,657, 34,904 episodes in patients by <1.2, <1.5, 90 Days and ALERTS definitions respectively.

8333 patients had first episodes occurring in 2011. The number of these having 2/3/4/5+ later episodes within 1yr were 2332/869/344/326, 2602/1095/485/609, 1534/331/71/17, 2728/1190/543/730 by <1.2, <1.5, 90 Days and ALERTS definitions respectively.

Conclusion / Implications
AKI episodes can be created in SAIL using SQL, and by adjusting the definition we see a variation in the number of episodes that a patient experiences. Once described, this cohort can be used to define a gold standard for AKI in future analysis.

Article Details

How to Cite
Davies, G., Scale, T., Akbari, A., Chess, J. and Lyons, R. A. (2020) “Defining Acute Kidney Injury Episodes”, International Journal of Population Data Science, 5(5). doi: 10.23889/ijpds.v5i5.1624.

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