Patients who experience acute kidney injury (AKI) while hospitalized face increased risk for morbidity and mortality after discharge. The increased risk of development and progression of chronic kidney disease (CKD) and death after an AKI event is associated with the severity, duration, and frequency of AKI episodes, as well as preexisting CKD and other comorbidities.
Previous studies of administrative databases have been limited to study populations that were elderly or had limited demographic and geographic diversity, were conducted in countries with universal medical coverage, or have lacked a control group of hospitalized patients without AKI.
Ivonne H. Schulman, MD, and colleagues conducted a retrospective, propensity score-matched cohort study designed to quantify various short- and long-term outcomes of hospitalization with AKI. Results were reported in the American Journal of Kidney Diseases.
The study outcomes of interest were all-cause and selected-cause rehospitalizations and mortality within 90 and 365 days after index hospitalization. The researchers identified patients with prior continuous enrollment for at least 2 years hospitalized with and without a discharge diagnosis of AKI between 2007 and September 2020 in Optum Clinformatics, a national claims database.
A total of 471,176 patients hospitalized with AKI were propensity score-matched to 471,176 patients hospitalized without AKI. Following propensity-score matching, the cumulative incidence function method was used to estimate incidences of rehospitalization and death; Gray’s test was used to compare the incidences between the two groups. Cox models for all-cause mortality were used to test the association of AKI hospitalization for each outcome.
The cumulative incidence per 100 patients of all-cause hospitalization within 90 and 365 days after discharge was significantly higher in the propensity score-matched cases than in controls. The cumulative incidences per 100 patients of all-cause hospitalization within 90 and 365 days after index discharge were significantly higher among patients with and without preexisting CKD in propensity score-matched cases than in controls (P<.001).
Cumulative incidence curves show that the incidence of all-cause rehospitalization with 365 days after index discharge was higher in patents hospitalized with AKI (propensity score-matched cases) than in patients hospitalized without AKI (propensity score-matched controls). It was also higher in patients with preexisting CKD than in patients without preexisting CKD (P<.01).
Results of the Cox model for cause-specific hazards demonstrated an association between AKI and an increased risk of rehospitalization within 90 days (hazard ratio [HR], 1.62; 95% CI, 1.60-1.65). Associations of AKI with rehospitalizations within 365 days after the index discharge were similar. There were no significant differences in the association of AKI with all-cause rehospitalization between those with preexisting CKD and those without preexisting CKD.
The cumulative incidences per 100 patients of nearly all select-cause rehospitalizations within 90 and 365 days of index discharge were significantly higher among the propensity score-matched cases than among controls. The most common causes of rehospitalization within 90 and 365 days for the propensity score-matched cases were sepsis, heart failure, AKI, and pneumonia. For the propensity score-matched controls, the most common causes were sepsis, heart failure, and pneumonia.
Among patients with preexisting CKD, with the exception of cerebrovascular accident (CVA), the cumulative incidence per 100 patients for select-cause rehospitalization was significantly higher in propensity score-matched cases than in controls (P<.001). While there was no significant difference between groups in the rates of CVA within 90 days after index discharge, the rate was significantly higher for propensity score-matched cases than for controls within 365 days after discharge (P<.01).
There were associations between AKI and higher rates of rehospitalization for end-stage renal disease (HR, 6.21; 95% CI, 1.04-36.92), heart failure (HR, 2.81; 95% CI, 2.66-2.97), sepsis (HR, 2.62; 95% CI, 2.49-2.75), pneumonia (HR, 1.47; 95% CI, 2.37-1.57), myocardial infarction (HR, 1.48; 95% CI, 1.33-1.65), and volume depletion (HR, 1.64; 95% CI, 1.37-1.96) at 90 days after index discharge compared with the group without AKI. Findings at 365 days after index discharge were similar.
The cumulative incidences per 100 patients of all-cause mortality were significantly higher in the group with AKI compared with the group without AKI within 90 and 365 days of index discharge (P<.01). The monthly cumulative incidences of mortality were also higher in the propensity score-matched cases than in controls with and without preexisting CKD (P<.01).
In the Cox model fitted for cause-specific hazards, there was an association between AKI and a significant increase in all-cause mortality. The association was stronger within 90 days (HR, 2.66; 95% CI, 2.61-2.72) compared with 365 days (HR, 2.11; 95% CI, 2.08-2.14). The association between AKI and all-cause mortality was significantly weaker in patients with preexisting CKD than in patients without preexisting CKD within both 90 days and 365 days after index discharge.
The researchers cited some limitations to the study findings, including the use of observational data that resulted in an inability to infer causal relationships between the AKI hospitalizations and the outcomes included in the study, the potential for bias from unmeasured confounding, the lack of data on inpatient creatinine values, and due to the use of data for an insured population, the findings may not reflect the uninsured population, who are particularly vulnerable and may experience worse AKI outcomes.
In summary, the authors said, “We confirm and extend prior studies in showing the association between a hospitalization with AKI and adverse short- and long-term clinical outcomes in a broad and diverse group of hospitalized patients with and without preexisting CKD. Although the best posthospitalization AKI clinical management regimen is yet to be determined, these results underscore the immediate need for close posthospitalization monitoring of individuals with AKI.”
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