Association of Age with Risk Factors for AKI

Age is a determining factor for acute kidney injury (AKI); however, according to Sandra L. Kane-Gill, PharmD, MSc, and colleagues, the risk for AKI in older adults has not been systematically assessed. The researchers conducted a retrospective analysis of data from July 2000 through September 2008 to examine the exposures and underlying susceptibilities for AKI in older adults compared with younger adults [American Journal of Kidney Diseases. 2015;65(6):860-869].

Hospital costs associated with AKI are exceeded only by those associated with acute myocardial infarction and stroke. AKI is defined as a sudden decline in kidney function during hours to days originating in either the community or hospital setting. AKI is classified by the KDIGO (Kidney Disease: Improving Global Outcomes) system by increasing severity from stage 1 to stage 3. Stages are based on decreased urine output over time or increases in serum creatinine levels or both. Mortality rates increase proportionally with the severity of decrease in kidney function.

Across all races and ages, the incidence of AKI has increased from 2000 to 2008. Hospitalized patients with AKI have lengths of stay that are 2.4 times longer than those of patients without AKI. Hospital mortality rates among patients with AKI are as high as 60% in the intensive care unit (ICU) and 80% among patients requiring renal replacement therapy (RRT).

Patients who progress to AKI during hospitalization have a more than 4-fold increase in mortality; developing AKI predisposes patients to progression to chronic kidney disease and end-stage renal disease.

The recent increase in incidence in AKI is linked to the increasing size of the elderly population. Management of risk for AKI based on susceptibilities and exposures are recommended by the KDIGO guidelines. However, there are limited data on outcomes of older adults hospitalized with AKI, and it has not been determined which risk factors are most important in that population.

This study utilized the High-Density Intensive Care database that includes data on 45,655 adult patients admitted to one of eight ICUs (medical, cardiac, transplant, surgical, neurologic, and trauma) within a single tertiary-care academic medical center. Exclusion criteria were hemodialysis, peritoneal dialysis, or transplantation prior to hospital admission, baseline creatinine level ≥4 mg/dL, liver transplantation during the index hospitalization, insufficient information to determine AKI status, and unknown age. After applying exclusion criteria, the study cohort comprised 39,938 patients.

The researchers collected data for multiple susceptibilities and exposures, including age, sex, race, body mass, comorbid conditions, illness severity, kidney function at baseline, sepsis, and shock. They calculated area under the receiver operating characteristic curve (AUC) for prediction of AKI across age groups.

Of the cohort of 39,938 patients, 63.2% (n=25,230) were ≥55 years of age (older adults). Female sex, history of cardiac disease, diabetes, hypertension, and other morbid conditions were more common among the older adults (P<.001). History of cardiovascular disease was similar between groups (those 18-54 years of age and the older adults); however, estimated glomerular filtration rate ≤60 mL/min/1.73 m2 was more frequent in older adults.

Those in the younger group had more frequent use of calcineurin-inhibitors and antibiotics. Older adults were more frequent users of nonsteroidal anti-inflammatory drugs, diuretics, and angiotensin-converting enzyme inhibitors and/or angiotensin II receptor blockers.

A greater proportion of older patients with AKI received vasopressors, but more younger patients met criteria for suspected sepsis and received mechanical ventilation. Compared with younger patients, older patients were less likely to receive RRT (P<.001); recovery after RRT at 90 and 365 days was significantly better in younger adults compared with older adults (P<.001 for both). Predictors of recovery after RRT at 365 days were age, race, history of hypertension, and aminoglycoside: those with a history of hypertension who received an aminoglycoside or were older were less likely to recover.

Overall, 62.9% of patients (n=25,120) developed AKI; among those ≥55 years of age, 69.2% developed AKI. As age increased, fewer variables remained predictive of AKI and the model for older patients was less predictive (P<.001). Among patients ≥75 years of age, risk factors for AKI were drugs (vancomycin, aminoglycosides, and nonsterioidal anti-inflammatories), history of hypertension (odds ratio [OR], 1.13; 95% confidence interval [CI], 1.02-1.25), and sepsis (OR, 2.12; 95% CI, 1.68-2.67).

AUCs were 0.744 for patients 18 to 54 years of age (95% CI, 0.735-0.752), 0.714 for patients 55 to 64 years of age (95% CI, 0.702-0.726), 0.706 for patients 65 to 74 years of age (95% CI, 0.693-0.718) and 0.673 for patients ≥75 years of age (95% CI, 0.661-0.685).

The primary limitation to the study cited by the researchers was including only ICU patients; the results may not apply to non-ICU patients.

In conclusion, the researchers said, “The likelihood of developing AKI increases with age; however, the ability to predict patients at risk for AKI declines with age using established risk factors. Our study confirms that age is an independent risk factor for AKI, although this does not seem to be a function of existing underlying decreased kidney function. Older patients are more likely to develop AKI compared with younger patients, and their long-term outcomes are worse. The challenges in risk assessment for AKI in this vulnerable population suggest that early detection with the goal of preventing injury progression and promoting better resource utilization should be the focus of future research.”


Takeaway Points

  1. Patients who progress to AKI during hospitalization have a more than 4-fold increase in mortality; developing AKI predisposes patients to progression to chronic kidney disease and end-stage renal disease.
  2. Overall, 62.9% of patients developed AKI; among those ≥55 years of age, 69.2% developed AKI. As age increased, fewer variables remained predictive of AKI and the model for older patients was less predictive (P<.001).
  3. Among patients ≥75 years of age, risk factors for AKI were drugs (vancomycin, aminoglycosides, and nonsterioidal anti-inflammatories), history of hypertension, and sepsis.