## 3 Results
### Identification of New Cases of AKI by Expanding Time Windows  
The incidence of AKI detected was 7.4% (_n_ = 9357) using a 24-h observation window for Scr criteria 1a and 1b. Additional cases of AKI were detected during the \"48-h expansion\" from 24 to 48 h (5.5%, \(n\) = 6963). A further 2509 cases of AKI (2.0%) were identified by expanding criteria 1b from 48 h to 7 days (48-h to 7-day expansion); and an additional 3004 cases were identified by expanding Scr criteria 1a and 1b from 48 to 168 h (the \"168-h expansion\") (2.4%). The incidence of AKI detected therefore increased from 14.9% (_n_ = 18,829) by using the standard AKI KDIGO criteria to 17.3% (_n_ = 21,833) by using a 168-h observation window and thus captured a 16% (_n_ = 3004) relative increase in \"additional cases\" of AKI.  
\begin{table}
\begin{tabular}{l c c} \hline \hline \multicolumn{1}{c}{**Characteristic**} & \multicolumn{2}{c}{**Study Sample**} \\  & \multicolumn{2}{c}{**(_n_ = 126,367)**} \\ \hline
**Race** & & \\ Caucasian & 77,373 & 61.2\% \\ Black or African American & 24,403 & 19.3\% \\ Other & 24,591 & 19.5\% \\
**Estimated GFR using first SCr b**, mL/min/1.73 m2  & 3178 & 2.5\% \\
15 to 29 & 9801 & 7.8\% \\
30 to 44 & 9801 & 7.8\% \\
45 to 59 & 16,762 & 13.3\% \\
60 to 74 & 20,098 & 15.9\% \\
75 to 89 & 24,857 & 19.7\% \\
90 to 105 & 25,276 & 20.0\% \\
3\(\times\)105 & 26,395 & 20.9\% \\
**Chronic comorbid conditions c** & & \\ Hypertension & 84,771 & 67.1\% \\ Heart disease & 59,863 & 47.4\% \\ Congestive heart failure d  & 23,317 & 18.5\% \\ Diabetes & 38,835 & 30.7\% \\ Anemia & 18,706 & 14.8\% \\ Cancer & 16,106 & 12.8\% \\ Cerebrovascular disease & 13,301 & 10.5\% \\ Chronic kidney disease & 11,820 & 9.4\% \\ Other kidney/uninary tract disease & 24,703 & 9.0\% \\ Peripheral and visceral atherosclerosis & 8167 & 6.5\% \\ Liver disease & 7759 & 6.1\% \\ Pancreas disease (not diabetes) & 1326 & 0.5\% \\
**Admission sequence e** & & \\ First (index) admission for a patient & 83,938 & 66.4\% \\ Second admission for a patient & 21,700 & 17.2\% \\ Greater than second admission for a patient & 20,729 & 16.4\% \\ \hline \hline \end{tabular} GFR, glomerular filtration rate; IQR, interquartile range; Scr, serum creatinine; SD, standard deviation. All information is displayed at the level of hospital admission and not at the level of a unique patient. The conversion factor for units of Scr in mg/dL to umol/L is x88.4.. \({}^{\star}\) Admission to one of our community hospitals in the health system. b The 2009 Chronic Kidney Disease Epidemiology Collaboration (CKD-EP) creatinine-based equation and the first in-hospital serum creatinine were used to estimate glomerular filtration rate. Patients with an estimated glomerular filtration rate of \(<\)15 mL/min/1.73 m2 were excluded from the study. c Chronic comorbid conditions were restricted to International Classification of Diseases Ninth Revision Clinical Modification codes that were flagged as chronic conditions using the Agency for Healthcare Research and Quality (AHRQ) Chronic Condition Indicator (CCI) version 2015. The AHRQ diagnosis clinical classification system (CCS) version 2015 categories 11–43 or 45 for cancer, 49–50 for diabetes, 59–61 for anemia, 96 or 100–108 for heart disease, 108 for congestive heart failure (subgroup of heart disease), 98–99 for hypertension, 109–113 for cerebrovascular disease, 114 for peripheral and visceral atherosclerosis, 6 and 150–151 for liver disease, 152 for pancreas disease (other than diabetes), 156 and 159–164 for other kidney disease, and 158 for chronic kidney disease. Comorbid conditions are not mutually exclusive. d Congestive heart failure is a subgroup of heart disease. e These data are presented by hospital admission and the admission sequence variable provides information on how many times a patient was included in the study cohort. The study included 83,938 unique patients representing a total of 126,367 unique hospital admissions.  
\end{table}
Table 1: Cont.