In-Hospital Kidney Injury Results in Increased Mortality After Discharge
By Nancy Fowler Larson
Medscape Medical News
December 17, 2009 — Experiencing acute kidney injury (AKI) while hospitalized increases the risk for early death after release, even if kidney function is restored, according to a study published online December 17 in the Journal of the American Society of Nephrology.
"The majority of previous studies linking AKI to mortality examined in-hospital mortality only and did not address post-discharge morbidity and mortality. Studies examining post-discharge mortality have focused primarily on critically ill patients with AKI that requires dialysis," write Jean-Philippe Lafrance, MD, and Donald R. Miller, ScD, from the Center for Health Quality, Outcomes, and Economic Research, and Edith Nourse Rogers Memorial Veterans Hospital, Bedford, Massachusetts. "Consequently, it remains unclear whether AKI that does not require dialysis is associated with a higher long-term risk for all-cause mortality."
The researchers retrospectively analyzed existing data regarding 82,711 US veterans whose AKI did not require dialysis and who survived at least 90 days after discharge. They evaluated mortality risks with multivariable Cox regression models adjusting for demographics, comorbidities, medications, admission diagnosis, number of days hospitalized, mechanical ventilation, and estimated glomerular filtration rate (residual kidney function) after leaving the hospital. Baseline creatinine values, a mean of 3.5 for each patient, had decreased to 1.1 at the time of hospital release.
The results showed a significant mortality increase among those with AKI. During follow-up (mean duration, 2.34 ± 1.43 years), 150,231 patients died (17.4%). The crude cumulative risk for death was 29.8% for the AKI group compared with just 16.1% for those who did not have AKI.
"Whereas each successive addition of covariates to the model reduced the mortality risk estimate, AKI remained associated with a 41% increased risk for all cause mortality in the fully adjusted model (adjusted [hazard ratio] 1.41; 95% confidence interval [CI] 1.39 to 1.43). A risk gradient was found among the three AKI categories (adjusted [hazard ratio] 1.39 versus 1.51 versus 1.71, for AKIN stages I, II, and III, respectively, compared with no AKI), with severity of AKI associated with increasing risk for death (P < 0.001 for trend)," the authors write. "To our knowledge, this is the first study to attempt to disentangle the direct association of AKI with mortality independent of the short-term loss of kidney function induced by AKI."
There were several limitations of the study, including that:
The existing data were not gathered for the specific purpose of this research,
The cause-of-death information was unavailable, and
The serum creatinine test information used to evaluate AKI was incomplete.
Furthermore, only 4.9% of patients studied were women.
More extensive and longer-term research is needed to use these findings in a medical setting, according to the authors.
"Prospective studies that evaluate the clinical course (including changes in kidney function after 90 [days]) and optimal treatment of patients discharged after AKI are needed to improve outcomes," the authors write.
A Veterans Affairs research grant supported this study. Dr. Lafrance is supported by a KRESCENT Fellowship, and Mr. Miller has received research grant funds from Sanofi-Aventis.
J Am Society Nephrol. Published online December 17, 2009.
